Preheat the oven to 350°F (177°C). Grease a 9-inch square pan or line with parchment paper, leaving an overhang on the sides to lift the finished blondies out (makes cutting easier). Set aside.

Whisk the flour, baking powder, and salt together in a large bowl.

In a medium bowl, whisk the melted butter and espresso powder together. Whisk in the brown sugar until combined, then whisk in the egg, extra egg yolk, and vanilla extract. Pour the wet ingredients into the dry ingredients and whisk or stir until combined. Batter is pretty heavy and thick, so I usually use a silicone spatula. Fold in the chocolate.

Evenly spread batter into prepared pan. Bake for about 30-35 minutes, or until a toothpick comes out *mostly* clean. A couple moist crumbs are ok, as long as it’s not wet. Remove from the oven and cool blondies completely in the pan set on a wire rack.

Using a fork, mix the espresso powder and warm water together in a medium bowl. Whisk in the confectioners’ sugar and milk/cream. For thinner glaze, whisk in more milk/cream. For thicker glaze, whisk in more confectioners’ sugar.

Drizzle over cooled blondies. Lift the blondies out using the parchment paper overhang on the sides. Cut into squares.

Cover and store leftover blondies (with glaze) at room temperature for up to 2-3 days or in the refrigerator for 1 week. Blondies without glaze are fine covered at room temperature for a week.