Barefoot Contessa's Blueberry Crumb Cake

INGREDIENTS

• 1/4 cup granulated sugar
• 1/3 cup light brown sugar, lightly packed
• 1 teaspoon ground cinnamon
• 1/8 teaspoon ground nutmeg
• 1/4 lb unsalted butter, melted
• 1 1/3 cups all-purpose flour
• 6 tablespoons unsalted butter, at room temperature
• 3/4 cup granulated sugar
• 2 extra-large eggs, at room temperature
• 1 teaspoon pure vanilla extract
• 1/2 teaspoon grated lemon zest
• 2/3 cup sour cream
• 1 1/4 cups all-purpose flour
• 1 teaspoon baking powder
• 1/4 teaspoon baking soda
• 1/2 teaspoon kosher salt
• 1 cup fresh blueberries
• confectioners' sugar, for sprinkling