Maple Blueberry Buckle

Ingredients

• 1 cup (128g) all purpose flour
• 1/2 cup (100g) packed brown sugar
• 1/4 teaspoon cinnamon
• 1/8 teaspoon fine sea salt
• 6 tablespoons (85g) cold, unsalted butter, cubed
• 1 2/3 cup (213g) all purpose flour, sifted
• 2 teaspoons baking powder
• 1/2 teaspoon fine sea salt
• 1/2 teaspoon cinnamon
• 1/4 teaspoon ground nutmeg (preferably freshly ground)
• 1/2 cup (113g) unsalted butter, room temperature
• 3/4 cup (150g) packed brown sugar
• 1/4 cup (50g) granulated sugar
• 2 large eggs, room temperature
• 2 teaspoons pure maple extract
• 1/2 teaspoon pure vanilla extract
• 1/2 cup (118ml) whole milk, room temperature
• 1/3 cup (75g) sour cream, room temperature
• 1 1/2 cups (234g) fresh or frozen blueberries, divided
• 1 cup (120g) powdered sugar, sifted
• 1 tablespoon pure maple syrup
• 1 tablespoon (14g) unsalted butter, melted
• 1/2 teaspoon pure maple extract
• 1 dash fine sea salt
• 1-2 tablespoons (15-30ml) whole milk, room temperature