Toffee Cake

12 1.4-ounce Heath bars or similar chocolate-coated toffee candy bars
1/2 cup butter, at room temperature
1/2 cup sugar
1 cup dark brown sugar
2 cups flour
1 egg
1 teaspoon baking soda
1 teaspoon vanilla
1 cup buttermilk, at room temperature
1/8 teaspoon salt

Preheat oven to 350 degrees. Lightly grease a 13-inch by 9-inch pan.

Grind candy bars in food processor to preferred texture.

Combine butter, sugar, brown sugar, and flour in food processor. Process until mixed. Combine 1/2 cup of this mixture with candy in a bowl; mix well. Add egg, baking soda, vanilla, buttermilk, and salt to remaining flour mixture. Process until mixed. Pour into prepared pan. Spread with half of candy mixture.

Bake 20 minutes. Spread with remaining candy mixture.

Bake 10 to 20 minutes longer, until a tester inserted near the center comes out clean.