Preheat oven to 325°F (160°C), preferably convection
Line a 9-inch square pan with parchment paper sling
Melt butter in a pot over medium heat until water boils out
Stir butter as it browns, keeping milk solids from sticking to bottom
When butter smells like caramel and just starts browning, whisk in cocoa powder
Let cocoa boil for a minute, then remove from heat
Whisk in sweetened condensed milk until combined
Whisk in powdered sugar until fully dissolved
Whisk in salt, vanilla, and molasses
Whisk in egg yolk (or whole egg for cakey version)
For cakey version, whisk in baking powder
Whisk in flour until smooth
If using chocolate chips, let batter cool slightly first, then stir in
Pour batter into prepared pan without worrying about even distribution
Bake 30-40 minutes until toothpick comes out clean or slightly fudgy
Let cool thoroughly before cutting
