New England Blueberry Buckle

From the garden

• 3 cups ripe blueberries, picked over, stems removed · about 1 pound; frozen berries go in straight from the freezer, unthawed

From the pantry

• 2½ cups all-purpose flour · 2 cups for the cake, 1/2 cup for the streusel
• 2 tsp baking powder
• ¾ cup granulated sugar · for the cake batter
• ½ cup brown sugar · for the streusel
• 1 tsp ground cinnamon
• 10 tbsp butter · 6 tablespoons softened for the batter, 4 tablespoons cold for the streusel, plus more for the pan
• 1 egg · at room temperature
• ½ cup whole milk
• 1 lemon, zested (optional) · zest only, for lift; the juice is not needed here
• ½ tsp salt

1. Heat the oven to 375°F and butter a 9-inch square pan. Whisk the 2 cups of cake flour with the baking powder and the salt in one bowl and set it aside.
2. Cream the softened butter with the granulated sugar until pale and fluffy, about 3 minutes, then beat in the egg and the lemon zest until the mixture looks smooth rather than curdled.
3. Fold in the flour mixture and the milk in alternating additions, beginning and ending with flour. The batter stays thick, closer to a drop biscuit than a pourable cake, and that is correct.
4. Spread the batter into the pan and scatter the blueberries evenly over it. Rub the streusel flour, brown sugar, cinnamon, and cold butter together with your fingertips until crumbly, then strew the crumbs over the fruit.
5. Bake 45–55 minutes, until the streusel is deep gold and a skewer pushed into the cake between the berries comes out clean. Juice will be bubbling up through the buckled top.
6. Cool at least 30 minutes so the crumb sets, then cut into squares straight from the pan. Serve warm, with cream alongside if the berries picked tart.