Blueberry breakfast cake

Ingredients

• 2 cups all-purpose flour
• 1/2 cup sugar
• 2 teaspoons baking powder
• 1 egg, lightly beaten
• 1/2 cup milk
• 1/4 cup butter or margarine, softened
• 1 teaspoon grated lemon peel
• 2 cups fresh blueberries
• 1/3 cup sugar
• 1/4 cup all-purpose flour
• 1/4 cup finely chopped walnuts (I used ground hazelnuts I had in the freezer)
• 1/2 teaspoon ground cinnamon
• 3 tablespoons cold butter or margarine