Bittersweet Brownie Bites

¼ cup boiling water
1 tablespoon instant espresso granules or 2 tablespoons instant coffee granules
¼ cup bittersweet chocolate chips
6 tablespoons butter, melted
½ teaspoon vanilla extract
1 large egg
1 large egg white
1 ½ cups all-purpose flour (about 6 3/4 ounces)
1 ⅓ cups granulated sugar
½ cup unsweetened cocoa
1 teaspoon baking powder
¼ teaspoon salt
Cooking spray
2 teaspoons powdered sugar (optional)
Preheat oven to 350°.
Combine 1/4 cup boiling water and espresso in a medium bowl. Add chocolate chips, stirring until chocolate melts; cool slightly. Stir in butter, vanilla, egg, and egg white.

Lightly spoon flour into dry measuring cups; level with a knife. Combine flour and next 4 ingredients (through salt), stirring with a whisk. Add coffee mixture to flour mixture, stirring just until moist. Spoon batter into mini-muffin tins coated with cooking spray. Bake at 350° for 25 minutes or until a wooden pick inserted in center comes out clean. Cool in pan on a wire rack. Sprinkle with powdered sugar, if desired.