Double Chocolate Potato Brownies

3/4 cup butter (1 1/2 sticks)
3 (1 ounce) squares unsweetened chocolate
1 1/2 cups granulated sugar
4 eggs, at room temperature
1 teaspoon vanilla extract
1/2 teaspoon salt
1 cup mashed white potatoes (unseasoned) at
    room temperature (about 2 medium potatoes)
1 cup all-purpose flour
3/4 cup semisweet chocolate chips
3/4 cup walnuts, chopped

Preheat oven to 350 degrees F. Grease a 13 x 9-inch baking pan.

Melt butter and chocolate in medium saucepan over low heat until smooth. Let cool 15 minutes. Stir in sugar, eggs, vanilla extract and salt. Stir in potatoes until smooth. Add flour and stir to combine. Pour into prepared baking pan. Sprinkle with chocolate chips and walnuts. Bake until brownies are firm when lightly touched, 25 to 30 minutes. Cool on rack. Cut into squares to serve.

Makes 24 brownies.

NOTE: To cook potatoes, peel and cut into chunks. Cover with boiling water and cook until tender. Drain well and mash with fork until smooth.