grease and line an 8 inch square pan with parchment leaving overhang.
Mix batter
whisk flour cocoa baking powder salt and spices until uniform
whisk butter brown sugar and molasses until glossy
whisk in eggs one at a time then vanilla
fold in dry ingredients just until no dry streaks
fold in chocolate chips if using.
Bake and cool
spread batter evenly in pan
bake until edges are set and center is just barely firm and a toothpick shows moist crumbs 22 to 28 minutes
cool in pan 30 minutes then lift out and cool fully before slicing for clean squares.
Notes
1. Use dark brown sugar for deeper flavor; do not overbake or brownies will turn cakey; for extra soft texture rest covered overnight; substitute 1 4 cup oil for 1 4 cup of the butter if desired; add 1 tbsp espresso powder to intensify chocolate