Step 1

Preheat the oven to 350°F. Grease 2 standard muffin pans with nonstick spray. (See "tips," below for details on how to bake the brownie cookies without a muffin pan.)

Step 2

, To make the brownie batter: In a large microwave-safe bowl or in a saucepan set over low heat, melt the butter, sugar, salt, and espresso powder. Stir until the butter is melted and the sugar has dissolved. The mixture will become shiny.

Step 3

, Add the chocolate chips and stir until chips have melted; reheat gently if necessary. Stir until smooth and the mixture feels warm, not hot.

Step 4

, Add the eggs and vanilla, stirring until smooth.

Step 5

, Add the flour, cocoa powder, and baking powder and mix gently until no dry spots remain.

Step 6

, Portion the batter evenly into the prepared wells of the muffin pans (about 1 generous tablespoon per well). If using a tablespoon cookie scoop, use 1 level scoop per well.

Step 7

, To make the cookie batter: In a large microwave-safe bowl or in a saucepan set over low heat, melt the butter. Add the sugar and salt, stirring until well combined. If the mixture feels hot to the touch, allow it to cool for several minutes until it’s just warm.

Step 8

, Add the egg and vanilla, stirring until smooth.

Step 9

, Add the flour, baking soda, and baking powder. Mix gently until no dry spots remain.

Step 10

, Check the temperature of the batter: If it’s warm to the touch, let it cool briefly before adding the chocolate chips. (You don’t want them to melt while being stirred in.) When the batter feels close to room temperature, add the chocolate chips and mix until evenly distributed.

Step 11

, Portion the batter evenly into the prepared wells of the muffin pan (about 1 generous tablespoon per well), on top of the portioned brownie batter. If using a tablespoon cookie scoop, use 1 scant scoop per well; no need to wash off the brownie batter from prior scooping.

Step 12

, Bake the brownie cookies for 18 to 22 minutes, until the cookies are golden brown, set in the middle, and just starting to pull away from the sides of the pan.

Step 13

, Remove from the oven and allow the brownie cookies to cool in the pan for 15 minutes before removing. Enjoy warm or at room temperature.

Step 14

, Storage information: Store any leftover brownie cookies, covered, at room temperature for up to 1 week; freeze for longer storage.