Fresh Blueberry Coffee Cake

Ingredients

• 2 cups all-purpose flour
• 1/2 cup granulated sugar
• 2 teaspoons baking powder
• salt, to taste
• 1/4 cup butter, softened
• 1 egg, lightly beaten
• 1/2 cup milk
• 1 teaspoon lemon zest
• 2 cups fresh or frozen blueberries
• 1/3 cup granulated sugar
• 1/4 cup all-purpose flour
• 1/4 cup walnuts, finely chopped
• 1/2 teaspoon cinnamon
• 3 tablespoons butter, cold