Cookie Ingredients
2/3 cup unsalted butter
2 tablespoons vegetable oil
¾ cup sugar
1 egg
2 teaspoons vanilla extract
½ teaspoon salt
1/8 teaspoon baking soda
1 teaspoon baking powder
1/3 cup Coco
1 ¾ cup flour

Fudge Center Ingredients
14 oz sweetened condensed milk
1 ½ cup semisweet chocolate morsels
4 ½ tablespoons Coco
3 tablespoons unsalted butter
1 teaspoon vanilla extract

For the cookies: with an electric mixer beat the butter, oil and sugar until fluffy. Add the egg, vanilla and salt and beat until well blended. On low speed gradually add the baking soda, baking powder, coco and flour, mix just until evenly incorporated.

Divide the dough in half, Roll out each portion between two sheets of waxed paper, about 1/8th inch thick. Stack the dough with the waxed paper on a cookie sheet and refrigerate 45 minutes (or up to 24 hours).

Preheat oven to 350 degrees. Remove the wax paper from the dough and cut it into 2 inch squares or circles. Bake on greased cookie sheets, 6-9 minutes or until almost firm in the center. Allow the cookies to cool on the cookie sheet for 2-3 minutes then transfer to a cooling rack.

For the Fudge Centers: in a 1 quart saucepan stir together all ingredients except the vanilla over medium-low heat, stirring constantly. Once the mixture is melted and smooth immediately remove it from the heat and stir in the vanilla. Allow the mixture to cool a bit just until it thickens enough to spread. Immediately spread the fudge on one cookie, 1/3 inch thick, and then top with a second cookie and press down gently. If the fudge gets too thick you can rewarm it over low heat stirring constantly.