Pre-heat oven to 350 degrees. Grease bottom only of an 8 inch square baking pan. Melt chocolate in small saucepan or microwave, stirring occasionally until smooth. In a separate bowl, beat butter using a wire whisk until it becomes light, gradually adding sugar until well combined. Stir in eggs, one at a time, beating well after each. Add milk and molasses or corn syrup. Add chocolate. Beat well to combine. Stir in flour, baking powder, salt, nuts, vanilla and rum. Spread evenly in greased baking pan. Bake for 20 to 30 minutes or until toothpick inserted in center comes out nearly clean, being careful not to over-bake. Allow cooling before cutting into squares.