Mix together melted 1/4 C butter and 1/3 C flour, then place on medium heat until it thickens, stirring frequently. Once there are no lumps, whisk in the 1 C milk and stir until smooth. Set aside in a bowl to cool.
Melt 3/4 C butter and mix with cocoa powder and sugar.
Add the milk and flour mixture to the cocoa mixture and cook on medium, stirring continually, until the raw flour flavor is gone.
Remove from heat and add vanilla. Sift together salt, baking powder, and 3/4 cup flour, then add to the pot.
Spray large muffin tins or a 9x13 pan liberally with cooking spray and spread the mixture into the pan. If desired, sprinkle with chocolate chips.
Cook for about 20 minutes, until a toothpick comes out clean.