1. Preheat oven to 400 F.
2. Grease 8 muffin cups or line with paper muffin liners.
3. In a large bowl, combine flour, sugar, salt and baking powder.
4. Add egg, oil and milk: mix well.
5. Fold in diced peach and nectarine.
6. Fill each muffin tin to the top with the mixture.
7. Sprinkle a little brown sugar onto the top of each uncooked muffin.
8. Bake in preheated oven for 18 to 20 minutes.
9. Check muffins regularly after 15 minutes of baking.
10. Serve warm or cold.