Preheat oven to 350°F. Line an 8×8-inch pan with aluminum foil and lightly spritz with cooking spray; set aside.

In a medium bowl, whisk together flour, cocoa, instant coffee powder, baking soda, and salt until combined. Set aside.

Place chocolate and butter in a large microwave-proof bowl and melt in 30 second spurts, stirring in between each interval until completely melted. Set aside to cool a bit. (Alternatively, melt chocolate and butter in a saucepan set over low heat, stirring frequently until melted. Set aside to cool.)

Once the chocolate mixture is warm (not hot!), add eggs one at a time, whisking constantly to incorporate. Whisk vigorously for about 10 seconds to incorporate fully. Add sugar, vanilla, and Bailey’s and whisk until combined. Add the flour mixture into the chocolate mixture, folding until just combined.

Pour batter into the prepared pan, using a spatula to smooth out the top. Bake at for about 18-20 minutes, or until a toothpick comes out with a few moist crumbs attached. Let cool, and dust with powdered sugar if desired.