Ingredients

• 1/3 cup plus 1/2 cup sugar
• 1/4 cup water
• 1 tablespoon fresh lemon juice
• 1 teaspoon cornstarch
• 10 oz blueberries (2 cups)
• 1 cup all-purpose flour
• 1 3/4 teaspoons baking powder
• 1 teaspoon salt
• 1 large egg
• 1/2 cup whole milk
• 1 stick (1/2 cup) unsalted butter, melted and cooled slightly
• 1 teaspoon vanilla

Instructions

1. Put oven rack in middle position and preheat oven to 375°F. Butter a 9-inch square baking pan.
2. Stir together 1/3 cup sugar with water, lemon juice, and cornstarch in a small saucepan, then stir in blueberries. Bring to a simmer, then simmer, stirring occasionally, 3 minutes. Remove from heat.
3. Whisk together flour, baking powder, salt, and remaining 1/2 cup sugar in a medium bowl.
4. Whisk together egg, milk, butter, and vanilla in a large bowl, then add flour mixture, whisking until just combined.
5. Spoon batter into baking pan, spreading evenly, then pour blueberry mixture evenly over batter (berries will sink). Bake until a knife inserted into center of cake portion comes out clean, 25 to 30 minutes. Cool in pan on a rack 5 minutes.