For the Cake
6tablespoons/86 grams unsalted butter, cut into pieces
¼cup/60 milliliters whole milk
2teaspoons pure vanilla extract
½teaspoon instant coffee or espresso (optional)
¾cup/165 grams packed dark brown sugar
1cup/128 grams all-purpose flour
⅓cup/32 grams unsweetened natural cocoa powder
1teaspoon kosher salt (such as Diamond Crystal)
½teaspoon baking powder
¼teaspoon baking soda
For the Topping
½cup/110 grams dark brown sugar
¼cup/24 grams unsweetened natural cocoa powder
¼teaspoon kosher salt (such as Diamond Crystal)
¾cup boiling water
Ice cream, to serve
Step 1

Prepare the cake: Add the butter to a 1½- to 2-quart microwave-safe soufflé dish or casserole, then melt the butter in short bursts in the microwave.
Step 2

Whisk in the milk, vanilla and instant coffee, if using. Whisk in the brown sugar, then add the flour, cocoa, salt, baking powder and baking soda and whisk until just combined.
Step 3

Make the topping: In a small bowl, whisk together the brown sugar, cocoa powder and salt. Sprinkle over the cake batter.
Step 4

Pour the boiling water over the top.
Step 5

Cook in the microwave at full power until you can see the set cake start to emerge through the sauce in various spots and the sauce has thickened, 5 to 7 minutes. (It’s OK to periodically stop and check doneness partway through cooking.) The cake will continue to set as it cools.
Step 6

Serve warm, with ice cream

TND TND