Step 1

Whisk sugar, flour, cinnamon, nutmeg, and salt in a medium bowl. Add butter and rub in with your fingers until mixture comes together in large clumps; set aside.

Step 2

Preheat oven to 350°. Butter and flour pan. Whisk baking powder, salt, and 1 1/2 cups flour in a medium bowl.

Step 3

Using an electric mixer on high speed, beat sugar and 1/4 cup butter until very light and fluffy, about 5 minutes. Beat in egg and vanilla just to combine, about 2 minutes. Reduce speed to low and gradually add dry ingredients, then cream; mix just to combine. Gently fold in blueberries. Scrape batter into prepared pan, smooth top, and place pan on a rimmed baking sheet. Evenly sprinkle topping over.

Step 4

Bake buckle until top is golden brown and a cake tester inserted into the center comes out clean, 80–90 minutes. Transfer pan to a wire rack and let cool before unmolding and serving.