Preheat oven to 350 degrees F. Line a 12 cup muffin pan with paper liners.
In a large bowl, beat with an electric mixer, 1 stick butter, peanut butter, granulated sugar, and 1/2 cup brown sugar, until creamy. Add eggs, milk, and vanilla, and beat until fluffy. Add 1-3/4 cups flour, baking powder, and salt; mix well. Spoon batter evenly into muffin cups.
In a small bowl, combine Streusel Topping ingredients with a fork until crumbly. Evenly spoon streusel mixture on top of batter. Bake for 20 to 25 minutes or until a toothpick inserted in center comes out clean. Let cool.