Preheat the oven to 350 F, and position a rack in the center of the oven. Spray an 8-inch springform pan with non-stick baking spray.
In the bowl of your stand mixer fitted with the paddle attachment, beat the softened butter with the sugar on medium speed for 3 minutes, until fluffy.
Scrape the bowl down, and add the ricotta cheese. Beat on medium speed for 5 minutes. This step aerates the ricotta for a fluffy cake crumb.
Add the eggs, one at a time, mixing well after each. Add the vanilla extract, lemon juice and lemon zest. The cake batter will look curdled at this point.
In a separate bowl, sift together the flour, baking powder and salt. Add the dry ingredients to the cake batter, and mix just until combined. Use a spatula to scrape everything up from the bottom to make sure the batter is evenly mixed.
Spread the cake batter into your prepared pan. Bake for about 50-55 minutes, until a cake tester comes out clean, and the top of the cake springs back when gently touched.
Set the pan on a cooling rack, cover loosely with a clean kitchen towel, and cool completely.
When the cake is cool, run a knife around the side of the pan, then release the collar. Turn the cake over onto a serving plate or cake pedestal, so the flat bottom side is facing up.
In a bowl, whisk together the icing ingredients until smooth. It should be fairly thick, but drizzly.
Immediately, pour the icing on top of the cake, and use a spatula to spread it towards the edges, gently nudging it over the edges of the cake.
Let the icing set and crust over (about 30 minutes) before slicing the cake and serving.
Store leftover cake in an airtight container at room temperature for 2 days, or in the refrigerator for up to 5 days.