Preheat the oven to 350°F. Grease a foil-lined 8×8-inch baking dish. Finely chop the chocolate into small chunks and set half aside. To a heatproof bowl, combine the butter and half of the chocolate. Set bowl over a saucepan of simmering water (do not let bottom of bowl touch water) Cook, stirring occasionally, until smooth and well combined.
Remove bowl from pan and stir in the molasses, granulated sugar, and brown sugar. Let cool slightly before whisking in the eggs. Fold in the flour, pumpkin pie spice, salt, and reserved chocolate chunks. Spread batter in the baking dish. Bake 30 min., until a toothpick inserted in center comes out clean. Let cool on wire rack.
Once cool, top with stencil and dust with the confectioners sugar to create a design. Cut into 2×2-inch squares.