Banana Coffee Cake

Name: Banana Coffee Cake
Ingredients: 5 tablespoons unsalted butter; 1/2 cup walnut pieces and halves; 1/2 cup all-purpose flour; 1/4 cup packed light brown sugar; 1/4 cup granulated sugar; 1 teaspoon ground cinnamon; 1/4 teaspoon freshly grated or ground nutmeg; 1/4 teaspoon kosher salt; 2 very ripe medium bananas; 1 large egg; 1/2 cup packed light brown sugar; 1/2 cup granulated sugar; 1/2 cup vegetable oil; 1/2 cup whole or 2% milk; 2 teaspoons vanilla extract; 2 teaspoons baking powder; 1 1/2 cups all-purpose flour