Rhubarb Crumble and Custard

This delicious Harry Potter inspired dessert pairs sweet and tart rhubarb crumble topped with buttery cinnamon oat streusel and creamy vanilla bean custard. The salty sweet crumble with the tart fruit filling and rich custard makes the most fantastic combination of flavors and textures. You’ll love this easy fruit crumble recipe!

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My husband loves rhubarb desserts, and coincidentally enough, after we bought our house in the winter, we discovered a rhubarb plant growing in the backyard when all the snow melted and spring came.  That plant is so hardy, that no amount of late spring snow can hurt it, and it thrives regardless.  So in the summer, I make rhubarb jam, pies, tarts, oatmeal bars, cakes and even ice cream and homemade liqueur with our fresh rhubarb. I often pair it with strawberries or apples, and freeze the rest to use throughout the winter.

Early spring is the best season for fresh rhubarb, so watch for it in your local grocery store between April and June. And if you can’t find it fresh, you may be able to get bags of frozen rhubarb.

For a fun bit of Harry Potter trivia, Harry’s first dinner at the headquarters of the Order of the Phoenix is followed by one of his favorite desserts: Rhubarb Crumble with Custard Sauce. I adapted my recipe from the one in The Unofficial Harry Potter Cookbook.

Ingredients

Rhubarb Crumble

• Rhubarb. Rhubarb is extremely tart, making it an excellent ingredient for sweet desserts. It breaks down and thickens when cooked.
• Granulated Sugar + Dark Brown Sugar. Granulated sugar in the filling sweetens the rhubarb, while brown sugar in the crumble topping adds a delicious rich flavor.
• All-purpose Flour. Most of the flour will go into the crumb topping, but a little flour helps to thicken the rhubarb filling.
• Lemon Zest. Enhances the flavor of the rhubarb.
• Baking Soda. Neutralizes the acidity and tartness of the rhubarb. Leave it out if you like a more tart rhubarb dessert.
• Cinnamon. Complements all the flavors in the crumble.
• Oats. Adds texture and crunch in the topping.
• Coarse Kosher Salt. Balances the sweetness.
• Unsalted Butter. Moistens the crumb topping and helps it to bake up crisp.

Vanilla Bean Custard

• Whole Milk + Cream. A combination of milk and cream makes the custard rich, creamy and luxurious.
• Granulated Sugar. Adds sweetness.
• Egg Yolks. The egg yolks add richness, as well as help to thicken the custard a little.
• Corn Starch. Thickens the custard.
• Coarse Kosher Salt. Balances the sweetness and enhances the flavor.
• Vanilla. If you can, use real vanilla beans. The black specks look gorgeous, and the flavor is incredible. You could also use vanilla bean paste or good-quality vanilla extract.
• Unsalted Butter. A touch of butter added at the end adds extra richness and flavor.

Instructions

Rhubarb Filling

• Preheat the oven to 350 and spray a deep dish pie pan or a 9 or 10-inch baking dish with non-stick spray.
• Toss all the filling ingredients together and spread into the pan.  Bake for 10 minutes while you make the crumble topping.

Crumble Topping

• In a bowl (I just use the same one I mixed the filling in), combine the flour, brown sugar, oats, cinnamon and salt. Drizzle with the melted butter and stir until moistened and crumbly.
• Remove the pan from the oven, and stir up the filling. Sprinkle the topping over the rhubarb.
• Return the pan to the oven, and bake for 40-45 minutes, until the filling is bubbling and the topping is golden brown.

Custard

• In a saucepan whisk together the sugar, salt and cornstarch.  Gradually whisk in the milk and cream, then the egg yolks and scraped vanilla bean seeds.
• Over medium heat, cook the custard, while whisking constantly, until thickened enough to coat the back of a spoon.  Remove from the heat and whisk in the butter.
• The custard can be served warm, but I prefer it chilled.  The cool, creamy custard spooned over the hot crumble is lovely.
• Pour the custard into a lidded container and refrigerate until needed. Stir the custard until smooth before serving with the rhubarb crumble.

Something I believe that the English do exceptionally well is custard.  And with their affinity for custard, they serve it up far more frequently than would occur to me to do, because really, when have you ever been served a side of custard with your cake or fruit crumble or pie instead of ice cream or whipped cream? Since custard is essentially an unchurned ice cream base, it really does pair perfectly with anything that you might top with a scoop of ice cream.

Frequently Asked Questions

Should I use fresh or frozen rhubarb?

• Either fresh or frozen rhubarb will work, depending on what’s available at your local grocery store or farmer’s market. You’ll typically find fresh rhubarb between April and June.
• You can also buy canned rhubarb in syrup, but I’ve never used it for baking, and I’m not sure if it works the same as fresh or frozen.

Are rhubarb leaves poisonous?

• Yes, the green leaves are inedible due to their high concentration of oxalic acid, and consuming the leaves can cause rhubarb leaf poisoning. They are not toxic to the touch, though, so simply trim the leaves off the stalks and discard.

Is rhubarb supposed to be green or red?

• The variety of rhubarb plant will determine if the stalks are red, green or a combination of both, but there’s actually very little difference in taste. Red stalks are certainly prettier for cooking and baking, but green stalks taste just as delicious.

How can I freeze fresh rhubarb?

• Every spring when I harvest stalks from our rhubarb plants, I bake with some of it right away, and freeze the rest for later. The process is simple.
• Trim and discard the leaves.
• Wash and dry the stalks.
• Chop the rhubarb (I usually dice it into 1/2 inch pieces) and place in freezer bags, labeled by weight (1-2 pounds per bag is ideal).
• Suck as much air out of the bags as you can and freeze until needed.

Should I thaw frozen rhubarb first before baking with it?

• It’s best to thaw frozen rhubarb first, so it doesn’t affect the baking time of your recipe.

Why is there baking soda in the rhubarb filling?

• Baking soda neutralizes acid. When combined with rhubarb, it helps to neutralize some of the acidity and bitterness of the rhubarb, so that you don’t need to use as much sugar to sweeten the rhubarb. You can certainly leave out the baking soda if you want your rhubarb crumble to taste more tart.

Can I pair another fruit with the rhubarb in this crumble?

• You certainly can! Strawberry rhubarb is a classic combination, but peaches are also delicious with rhubarb. If you add strawberries or peaches to your crumble, you’ll need to increase the flour in the filling by a few more tablespoons to thicken your filling, since those fruits contain more water. Apple rhubarb crumble is also wonderful.

What’s the difference between a crisp and a crumble?

• The main difference between a crisp and a crumble is in the streusel topping. Traditionally, crisps contain oats and crumbles do not. In a crisp recipe, the oats in the topping crisp up as the topping bakes, hence the name. Over time, though, the terms crumble and crisp have been used interchangeably, and the difference is negligible. My crumble topping recipe contains oats, and there you have it.

How long does the crumble stay fresh?

• Rhubarb crumble is best served warm, the day it’s made, but it still tastes great the next day, even cold. Leftovers should be covered and refrigerated, and eaten within 2 days.

Do I need to use real vanilla beans in the custard?

• If you can, use real vanilla beans. The black specks look gorgeous, and the flavor is incredible. You could also use vanilla bean paste or good-quality vanilla extract.

Is the custard supposed to be thick or thin?

• The consistency of this custard is thicker than a creme anglaise, but certainly isn’t thick enough to hold its shape in a custard pie or pudding pie. It’s meant to be a “spoonable” custard to serve next to the rhubarb crumble.

What else can I serve with the vanilla bean custard?

• The custard would also be fantastic served with pound cake or angel food cake, coffee cake, apple pie, or just a simple bowl of fresh fruit.

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