The floral character of poppy seeds shines when paired with blueberries in this rich dessert. Store any unused seeds in the refrigerator or freezer.
- 20 tbsp. unsalted butter, softened, plus more for pan
- 3 cups flour, plus more for pan
- 1 1⁄2 cups sugar
- 3⁄4 tsp. kosher salt
- 1⁄4 tsp. vanilla
- 4 cups blueberries
- 2 tbsp. fresh lemon juice
- 1⁄2 tsp. ground cinnamon
- 1 1⁄2 cups ground poppy seeds (available at Kalustyan's)
- 1⁄2 cup heavy cream
Heat oven to 350°. Butter and flour a 9" x 13" metal baking pan; set aside. Beat 16 tbsp. butter and 1⁄2 cup sugar on medium-high speed of a mixer until pale and fluffy, about 2 minutes. Add 2 1⁄2 cups flour and 1⁄2 tsp. salt; beat until just combined. Press dough into bottom and halfway up sides of prepared pan; chill for 20 minutes. Bake crust until lightly browned, about 12 minutes; let cool. Meanwhile, stir remaining butter, flour, and salt, 1⁄4 cup sugar, and vanilla in a bowl until coarse crumbles form; set streusel aside.
Heat remaining sugar, 3 cups blueberries, lemon juice, and cinnamon in a 2-qt. saucepan over medium-high heat; cook until berries burst, about 20 minutes. Remove from heat and stir in remaining berries; let cool. Stir together poppy seeds and cream in a bowl; spread evenly over cooled crust. Pour blueberry mixture over poppy seeds; sprinkle with streusel mixture. Bake until filling is bubbly and streusel is lightly browned, about 40 minutes. Let cool, cut into squares, and serve.