Over medium or medium/low heat, melt the butter in the stock pot.
Add the water, corn syrup, salt, nutmeg and sugar, pouring the sugar gently into the middle of the butter. Let the sugar start to dissolve and melt into the butter, then use your wooden spoon to gently stir the mixture. Avoid stirring the sugar against the side of the pot, as sugar crystals could cause the toffee to crystallize. When the sugar looks mostly dissolved, rinse off your spoon to rid it of sugar crystals. If you see any sugar crystals on the side of the pot, wash them down with a wet pastry brush.
Continue to cook the syrup, stirring constantly. If the temperature seems to be rising too quickly, turn the heat down a touch. You want to cook sugar over moderate heat that doesn't cook the sugar too quickly, or you risk burning it.
If you're using an accurate candy thermometer, watch as the temperature gets closer to the 300-310 F range for the hard crack stage (290-300 F at 5,000 feet elevation). If you're not using a thermometer, watch the subtle color changes of the sugar, as it starts to deepen in color and scent. Drizzle a small amount of syrup into the ice water, wait a few seconds, then scoop it out and test it between your teeth. If it's chewy and sticky, the sugar is not ready. If it crunches, it's reached the hard crack stage. It should take about 15-20 minutes to reach this stage.
Immediately, remove the pot from the heat, and stir in the vanilla and 1 cup of the chopped almonds. It's normal for the syrup to hiss a little at this point.
Working quickly, pour the mixture onto the parchment lined baking sheet, and use a spatula to spread it out into a slab. The toffee will start to harden quickly, so you have to move fast.
Sprinkle the chocolate chips over the hot toffee. Wait a few minutes until they are glossy and soft, then use an offset spatula to spread the melted chocolate out to cover the toffee in a thin layer.
Sprinkle the chocolate with the remaining 1/4 cup of chopped almonds. If you like, sprinkle the top with a little flaky finishing salt, such as Maldon.