Preheat oven to 350 degrees. Spray a 9-inch square baking pan with cooking spray. Line the bottom with parchment paper and spray the paper. Set pan aside.

Combine the butter and sugar in the bowl of a stand mixer fitted with the paddle attachment. Cream on medium speed until light and fluffy. Gradually add the flour and mix until combined. Mix in hazelnuts until combined, then press into an even layer in the bottom of the prepared pan. (It will seem like there won’t be enough to cover the whole bottom; just keep going and you’ll get there.) Set aside.

Combine the butter and chocolate in a microwave-safe bowl and heat in 30-second intervals, stirring after each interval, until chocolate is melted and mixture is smooth. Cool.

Combine the eggs, sugars, vanilla, and espresso powder (if using) in a large mixing bowl. Whisk until blended. Stir in the cooled chocolate and Frangelico. Gradually whisk in the flour and salt, mixing until smooth. Fold in the hazelnuts. Pour filling over crust and smooth into an even layer with a rubber spatula. Bake for 22 to 25 minutes, until a cake tester inserted into the center comes out clean. (Don’t overbake them.) Cool completely on a wire rack before proceeding with the recipe.

Place the butter in the bowl of a stand mixer fitted with the paddle attachment and mix until smooth. Add remaining ingredients and beat on medium speed until smooth and creamy. (If frosting is too thick, add additional Frangelico or milk to make it spreadable.) Spread over cooled brownies, then refrigerate for 30 minutes.

Combine the chocolate and coconut oil in a small microwave-safe bowl. Heat in 15-second intervals, stirring after each interval, until chocolate is melted and mixture is smooth. Cool slightly, then spread over the frosting. Refrigerate until glaze is set, then slice into bars and serve. (Freeze leftovers, tightly wrapped, for up to 3 months.)