Preheat oven to 400°F (200°C). Line a baking sheet with parchment paper.

Whisk together whole wheat flour, all-purpose flour, baking soda, salt, and brown sugar.

In another bowl, mix molasses, melted butter, and buttermilk.

Combine wet and dry ingredients, stirring gently until a soft dough forms.

Shape dough into a round loaf and place on prepared baking sheet.

Score a deep cross on top with a knife.

Bake 35–40 minutes until browned and hollow-sounding when tapped.

Cool on a wire rack before slicing and serving.