recipe from joythebaker.com

     adapted from Gourmet

2 sticks (1/2 lb) unsalted butter
2 cups packed light brown sugar
1 tsp pure vanilla extract
2 large eggs
1 1/2 cups all-purpose flour
3/4 tsp baking soda
1/2 tsp salt
2 cups of your favorite candy bars, roughly chopped (We used Reese's Peanut Butter Cups, Heath Bar, and Peanut Butter M&M's)

Preheat oven to 350°F with rack in middle. Butter and flour a 13- by 9-inch baking pan.

Melt butter in a 3-qt heavy saucepan over low heat, stirring, until smooth. Remove from heat and cool to lukewarm. Whisk in brown sugar and vanilla. Whisk in eggs 1 at a time until mixture is glossy and smooth.

Whisk together flour, baking soda, and salt, then whisk into butter mixture. Stir in candy pieces reserving 1/2 cup to sprinkle on top.

Spread in pan and sprinkle with remaining 1/2 cup candy. Bake until a pick inserted in center comes out clean, about 35 minutes. Cool completely.