As the person who tests many of the recipes we publish, Amy Hamel has been asked to cook any number of dubious dishes. Still, even she was wondering what we were thinking when we asked her to develop a chocolate cake that could be baked in a slow cooker. Why bake in a slow cooker? It's a fun novelty, and kids love the whole idea, but the real proof is in the tasting. Drawing from a number of hot-fudge-brownie cake variations, Amy created a dessert so moist and chocolaty, "it's like getting to lick the batter from a whole cake," as one of our tasters said. But Amy's daughters may have offered the most eloquent testimony. They said nothing, but simply hovered over the crock, each with a spoon in hand and a chocolaty smile on her face.
Coat the inside of a 2 1/2- to 5-quart slow cooker with cooking spray. (Note: the cake's cooking time and final appearance will vary depending on your crock's size.)
Whisk together the flour and baking powder in a medium bowl and set aside. In a large bowl, melt the butter and chocolate in the microwave or over a pan of simmering water and mix well.
Whisk in the 2/3 cup of sugar, 3 tablespoons of cocoa, vanilla extract, salt, milk, and egg yolk. Add the flour mixture and stir until thoroughly mixed.
Pour the batter into the slow cooker and spread it evenly. In a medium bowl, whisk together the remaining sugar (white and brown), cocoa, and hot water until the sugar is dissolved.
Pour the mixture over the batter in the slow cooker. Cover and cook on high for 1 to 2 hours, depending on the size of the crock pot.
Even when done, the cake will be very moist and floating on a layer of molten chocolate, but you'll know it's ready when nearly all of the cake is set and the edges begin to pull away from the sides of the pot. (As you check, try not to let the condensed steam from the lid drip onto the cake.)
When it's done, turn off the power and remove the lid. Let it cool for 25 minutes, then serve it in bowls topped with whipped cream or ice cream. Makes 6 to 8 servings.