Oatmeal Sandwich Cookies With Creamy Peanut Butter Filling

Name: Oatmeal Sandwich Cookies With Creamy Peanut Butter Filling
Ingredients: 1/2 cup (1 stick) unsalted butter, softened; 1 cup brown sugar, packed; 1 large egg; 1 teaspoon vanilla extract; 1 1/4 cups uncooked oats; 1 cup all-purpose flour; 1/2 teaspoon baking powder; 1/2 teaspoon baking soda; 1/2 teaspoons salt; 1 teaspoon ground cinnamon; 1/4 teaspoon ground nutmeg; 1/2 cup chopped pecans; 3 tablespoons unsalted butter, at room temperature; 1/2 cup smooth peanut butter; 1 cup powdered sugar; 3-4 tablespoons milk