Toffee Coffee Dark Chocolate Brownies

My hubby loves coffee.  He drinks it like it's water.  He also loves dark chocolate.  So he went ga-ga over these brownies.  He did prefer it without the frosting, but I liked it with and since I was doing the baking, guess who won?  :)

Toffee Coffee Dark Chocolate Brownies
Adapted from Better Homes & Gardens
{ Makes: 20 brownies; Prep: 25 min.; Bake: 35 min. }

Ingredients
1 19.8- or 21-ounce package dark chocolate brownie mix
1/2 cup toffee pieces
2 tablespoons instant espresso powder or instant coffee crystals
2/3 cup walnuts, chopped (optional)

Directions:

1. Preheat oven to 350 degrees F. Grease a 9-inch square baking pan and set aside.
2. Prepare brownie mix according to package directions, except stir the 1/2 cup toffee pieces, the espresso powder, and chopped walnuts into batter. Spread batter into prepared pan.
3. Bake in preheated oven for 35 minutes.  In the meantime, prepare frosting (see instructions below). 
4. Once brownies are done baking, cool in pan on a wire rack.  Remove baked mixture from pan.  Spread frosting onto cooled brownies and sprinkle with chopped walnuts.  Cut into bars.  Makes 20 brownies.

TO STORE:  Place bars in a single layer in an airtight container; cover.  Store in the refrigerator for up to 3 days.

For Frosting:
1  cup  (1/2 lb.) unsalted butter, at room temperature
4  cups  (1 lb.) powdered sugar, sifted
1/8  teaspoon  salt
2  tablespoons  milk
2  teaspoons  vanilla

Preparation:
In a bowl, with a mixer (preferably fitted with whisk attachment) on low speed, beat butter, 2 cups powdered sugar, and the salt until blended.  Add milk and vanilla; beat until blended. Add remaining powdered sugar, 1 cup at a time, beating until incorporated.  Turn mixer to high speed and beat frosting until fluffy and smooth.