In a large saucepan, combine granulated sugar, butter, and cocoa powder.

Heat over medium heat, stirring until butter melts and ingredients are combined.

Remove from heat.

Add eggs and 1 teaspoon vanilla.

Beat lightly until just combined.

In a separate bowl, whisk together flour, baking powder, and baking soda.

In another bowl, stir together milk, Irish whiskey, and instant coffee crystals.

Alternately add the flour mixture and milk mixture to the chocolate mixture, beating by hand after each addition.

Stir in chopped walnuts.

Pour the batter into a greased 15x10x1-inch baking pan.

Bake in a preheated 350°F (175°C) oven for 15 to 20 minutes, or until a toothpick inserted near the center comes out clean.

Cool in the pan on a wire rack.

For the Irish Coffee Glaze, in a bowl, stir together sifted powdered sugar, cocoa powder, Irish whiskey, and vanilla.

Stir in brewed coffee, 1 tablespoon at a time, until the glaze reaches a drizzling consistency.

Drizzle the glaze over the cooled brownies.

If desired, sprinkle with additional chopped walnuts.