Czech Blueberry-Poppy Seed Squares | Saveur

Ingredients

• 20 Tbsp. softened unsalted butter, divided, plus more for greasing
• 1½ cups sugar, divided
• 3 cups all-purpose flour, divided, plus more for dusting
• ¾ tsp. kosher salt, divided
• ¼ tsp. vanilla extract
• 4 cups blueberries, fresh or frozen, divided
• 2 Tbsp. fresh lemon juice
• ½ tsp. ground cinnamon
• 1½ cups ground poppy seeds (see headnote)
• ½ cup heavy cream