8 ounces unsweetened chocolate
8 ounces unsalted butter
5 eggs, at room temperature
2 teaspoons vanilla extract
¼ teaspoon salt
1 tablespoon instant coffee or espresso
3½ cups sugar
1-2/3 cup all-purpose flour
2 pounds peppermint patties
1. Preheat the oven to 425 degrees F. Line a 9 x 13-inch baking pan with foil, shiny side down. Smooth the foil then butter it lightly or coat it with nonstick spray.
2. Chop the chocolate and cut the butter into cubes, then warm them together in a medium bowl set over a pan of barely simmering water, stirring occasionally. Remove from heat as soon as both are melted and smooth.
3. In the bowl of a stand mixer fitted with the whisk attachment or by hand, whip the eggs, vanilla, salt, instant coffee, and sugar on high speed for about ten minutes until foamy and stiff.
4. By hand, stir in the chocolate mixture, then the flour.
5. Smooth half of the batter into the pan. Place a layer of peppermint patties over the chocolate, breaking them into pieces to fill in any large gaps.
6. Pour the rest of the batter over the patties and smooth the top.
7. Bake the brownies for 35 minutes, rotating the brownies midway during baking. When the brownies are done, they will have a firm crust on top but a toothpick inserted into the center should come out wet. Do not overbake the brownies.
8. Let the brownies cool completely, then lift them out of the pan and slice into rectangles.
Storage: The brownies will keep at room temperature for up to three days. They can be frozen, well-wrapped, for up to two months.