12 Tablespoon(s) butter, softened
1 Cup(s) granulated sugar
1 Cup(s) light brown sugar, packed
2 Each(s) eggs
1 Cup(s) mashed potatoes, at room temperature
1 Teaspoon(s) vanilla extract
2 1/2 Cup(s) all-purpose flour
1/4 Cup(s) unsweetened cocoa powder
1 Teaspoon(s) salt
1 Teaspoon(s) baking soda
1 Cup(s) buttermilk
1 Cup(s) semisweet chocolate chips
1 Cup(s) chopped pecans
1 Tablespoon(s) confectioner's sugar for dusting
Heat teh oven to 350F. Grease a 10x15 baking pan and dust with flour. In a large bowl using an electric mixer, beat the butter with both sugars until light and fluffy. Beat in the eggs. Add the mashed potatoes and vanilla and continue to beat until smooth.
In a mixing bowl, sift or whisk together the flour, cocoa, salt and baking soda. With the mixer on medium speed, add the flour mixture alternately with the buttermilk, beating just until smooth. Stir in the chocolate chips and nuts. Scrape the batter into the prepared pan, smoothing the top.
Bake in the preheated oven until the top is springy when lightly touched and a tester inserted in the center comes out clean, 22 to 25 minutes. Cool in the pan on a wire rack for about 20 minutes. While still warm, cut into 24 or 36 squares. Dust with the powdered sugar before serving.