Preheat oven to 350 degrees. Line bottom of 8x8-inch baking pan with aluminum foil. Lightly butter foil.
Combine chunked butter and chocolate in microwave-safe bowl. Microwave in short intervals, about 30 seconds each, stirring in between until fully melted and smooth.
Whisk in sugar, eggs, vanilla, and espresso powder. Fold in flour and salt until no dry streaks remain.
Spread batter in even layer in prepared baking pan. Bake 30 minutes, until just set. Remove from oven and cool completely. Cut cooled brownies into small chunks.
Pour heavy cream into an electric mixer bowl. Whisk on medium to high speed until stiff peaks form. Transfer to separate bowl; set aside.
Return mixer bowl to base. In mixer bowl, combine mascarpone and powdered sugar. Beat on medium to high speed until smooth and fluffy, about 2 minutes. Blend in peppermint extract. Fold 1/3 of whipped cream into mascarpone mixture with spatula to lighten.
Gently fold in remaining whipped cream until evenly incorporated. In 8 individual trifle dishes or small mason jars, layer brownie pieces, whipped mascarpone, and sprinkle of crushed peppermint candy. Repeat layers. Refrigerate until ready to serve.