Preheat the oven to 350 degrees.
Mix softened butter, sugars, eggs, corn syrup, and peppermint extract in a mixing bowl.
Mix flour, cornstarch, cocoa, and salt in a second bowl or measuring cup.
Pour batter into an 8x8 lined baking pan.
Bake for 20-22 minutes
While the brownies are in the oven, prepare the frosting. Over medium heat, melt whipping cream, butter, chocolate chips, and peppermint extract in a saucepan.
Remove the brownies from the oven and immediately pour the frosting over the brownies.
Top evenly with sprinkles and chopped-up peppermint candies immediately following adding the frosting.
Let the brownies cool completely in the fridge before cutting them into squares.
Serve.