Set a heatproof bowl over a saucepan of simmering water over medium low heat. Add the chocolate and butter and stir occasionally as they melt together. Remove from heat as soon as chocolate is completely melted. Stir until smooth.

In the bowl of a stand mixer fitted with a whisk attachment, beat the eggs, vanilla, espresso or instant coffee, sugar, and salt on high until stiff, about 6-8 minutes. Fold in the chocolate mixture by hand, followed by the flour.

Spread half of the brownie mixture into the prepared baking dish. Place the mint candies evenly over the batter. Spread the remaining brownie batter over the top of the candies. Bake for 35 minutes, do not over bake. Edges should be crisp but middle should still be very soft. Let cool for 10 minutes, then lift brownies out of the dish with the aluminum foil to cool completely.

Brownies will keep at room temperature in a air tight container for several days, or tightly wrapped in the freezer for several weeks.