Microwave Chocolate Pudding Cake

• 6 tablespoons/86 grams unsalted butter, cut into pieces
• 1/4 cup/60 milliliters whole milk
• 2 teaspoons pure vanilla extract
• 1/2 teaspoon instant coffee or espresso (optional)
• 3/4 cup/165 grams packed dark brown sugar
• 1 cup/128 grams all-purpose flour
• 1/3 cup/32 grams unsweetened natural cocoa powder
• 1 teaspoon kosher salt (such as Diamond Crystal)
• 1/2 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/2 cup/110 grams dark brown sugar
• 1/4 cup/24 grams unsweetened natural cocoa powder
• 1/4 teaspoon kosher salt (such as Diamond Crystal)
• 3/4 cup boiling water

Ice cream, to serve

1. Prepare the cake: Add the butter to a 1 1/2- to 2-quart microwave-safe soufflé dish or casserole, then melt the butter in short bursts in the microwave.
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.
3. Make the topping: In a small bowl, whisk together the brown sugar, cocoa powder and salt. Sprinkle over the cake batter.
4. Pour the boiling water over the top.
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.
6. Serve warm, with ice cream.