Good-Cooking - Banana Walnut Upside-Down Cake

Ingredients

• 1 cup golden brown sugar, packed
• 1/4 cup unsalted butter
• 3 tablespoons pure maple syrup
• 1/4 cup walnuts, coarsely chopped
• 4 large ripe bananas, peeled and cut diagonally into 1/4-inch slices
• 1 cup all-purpose flour
• 2 teaspoons baking powder
• 1/2 teaspoon cinnamon
• 1/4 teaspoon salt
• 3/4 cup granulated sugar
• 6 tablespoons unsalted butter, room temperature
• 1 large egg
• 1/2 teaspoon vanilla extract
• 6 tablespoons milk