In the 8x8 inch baking pan, melt the butter and chocolate chips on the stove top, over medium heat, stirring constantly. Remove from the heat, and stir in the coffee, egg and yolk. Sift together the flour, sugar, and baking soda, stir into the chocolate mixture. Then stir in the vanilla and coffee liqueur.
Bake for 20 to 25 minutes in the preheated oven. Cool slightly and dust with confectioners' sugar. Cut into squares.