Preheat oven to 350°F and spray 12 muffin tins with non-stick cooking spray. Combine dry ingredients in a medium bowl, reserving 1 tablespoon brown sugar; mix well and set aside. Stir together cream cheese and the reserved 1 tablespoon brown sugar. When well blended, fold in 1/4 cup peaches. Add milk, oil, vanilla and egg to dry ingredients, mixing just until dry ingredients are moistened. Lightly stir in remaining peaches and walnuts. Spoon 3/4 of the mixture into prepared muffin tins. Place a teaspoonful of the cream cheese mixture in the center of each then spoon remaining batter over the top. Bake for 20 to 25 minutes or until a toothpick inserted into the center comes out clean.