To make the brownies:
Preheat the oven to 350 degrees. Line a 9”x13” baking pan with a large piece of foil with 2” overhang on all sides of the pan. Grease lightly with baking spray or oil.
Place a large bowl over a saucepan over medium-low heat with a small amount of simmering water in it. Put the chocolate and butter into the bowl and stir regularly until melted. Remove from heat and set aside briefly. In a separate small bowl, stir together the sweetened condensed milk and eggs. Whisking briskly, add the sweetened condensed milk mixture to the chocolate and butter mixture until well combined. Add the vanilla and sugar, stirring to combine. In a small bowl, combine the flour, cocoa powder, salt, and baking powder. Add the dry ingredients to the chocolate mixture and fold to combine. Stir in the mini chocolate chips.
Spread the mixture into the prepared pan and bake in the preheated oven for about 25-30 minutes or until the edges are well set and a toothpick inserted comes out only with a few moist clumps. Be careful not to overbake. Allow the brownies to cool completely.
To prepare the topping:
Melt the semisweet chocolate in a double boiler, similarly to the chocolate for the brownies. Spread the chocolate in an even, thin layer on the brownies. Place the pan in the fridge to set up while you repeat this process with the white chocolate. Melt it gently over very low heat (white chocolate will seize if it gets too hot!) and then spread evenly over top of the cooled, set semisweet chocolate. Sprinkle the top of the brownies with the peppermint pieces and allow to set completely in the fridge prior to slicing. Enjoy!