Heat oven to 350°F. Grease and line a 9x5-inch loaf pan.
Stir crumble flour, brown sugar, cinnamon, and salt in a bowl.
Drizzle in melted butter and toss until small clumps form. Chill.
Whisk batter flour, baking powder, baking soda, and salt in a large bowl.
Whisk buttermilk, eggs, granulated sugar, melted butter, vanilla, and orange zest until smooth.
Pour wet into dry and fold just until a few streaks remain.
Fold in chopped cranberries gently to avoid overmixing.
Spread batter in the pan and smooth the top.
Scatter crumble over batter. Add pecans on top if using. Press lightly.
Bake 50–60 minutes, until golden and a tester comes out clean.
Cool 15 minutes in pan. Lift out and cool completely before slicing.