Blueberry Crumb Cake

INGREDIENTS

5 tbsp

unsalted butter, at room temperature

1/4 cup

sugar

1/3 cup

(packed) light brown sugar

1/3 cup

all-purpose flour

1/4 tsp

salt

1/2 cup

chopped walnuts

1 pint

blueberries (preferably fresh, or frozen, not thawed)

2 cups

plus 2 teaspoons all-purpose flour

2 tsp

baking powder

1/2 tsp

baking soda

1/4 tsp

salt

1/4 tsp

ground cinnamon

1/8 tsp

freshly grated nutmeg

2/3 cup

sugar

Grated zest of 1/2 lemon or 1/4 orange

3/4 stick

unsalted butter, at room temperature

large eggs, at room temperature

1 tsp

pure vanilla extract

1/2 cup

buttermilk