Equipment:

Toaster or regular oven

Mini metal square or round pie pan

Brush

Small mixing bowl

Small whisk or fork

Small spatula

Arrange a rack in the middle of a regular or toaster oven and heat to 350 F. Place the butter in a mini square or round metal pie pan, and place the pan on top of the toaster oven or inside the regular oven as it heats to melt. Pour the melted butter into a small heatproof bowl. Use a brush to coat the pan with the residual butter left in the pan; set aside.

Whisk together the dry ingredients: flour, brown sugar, sugar and cocoa powder in a small bowl until thoroughly combined.

Add the wet ingredients: melted butter, egg yolk, coffee or water and vanilla. Stir with a rubber spatula to combine. Do not overmix.

Pour the batter into the prepared pan. Top with chocolate chips or walnuts if using. Bake for 15 minutes for a gooey center or 20 minutes for a cake-like brownie.

Remove from the oven and cool for 5 minutes before enjoying. Serve with ice cream, if desired.

Recipe notes: Need a self-rising flour substitute? Whisk together 1 cup all-purpose flour, 1 1/2 teaspoons baking powder and 1/4 teaspoon fine salt. Measure out 2 tablespoons for the brownie. The remaining can be stored in an airtight container for future use.

(Meghan Splawn is the associate food editor for TheKitchn.com, a nationally known blog for people who love food and home cooking. Submit any comments or questions to editorial@thekitchn.com.)