Preheat oven to 350°F / 175°C. Grease a 9×5 loaf pan.
Whisk flour, sugars, baking powder, salt.
Add milk, peanut butter, vanilla. Mix until just combined.
Spread into pan, sprinkle sugar if using.
Bake 50–60 minutes until toothpick comes out clean.
Cool 15 minutes, remove, slice.
For molasses glaze: Melt butter, whisk in molasses and milk until warm.
Remove from heat and whisk in powdered sugar until smooth.
Stir in vanilla and salt. Add optional cinnamon or ginger if desired.
Serve bread warm with molasses glaze.
