1. Preheat your oven to 350°F (175°C). Grease and line a 9-inch round cake pan with parchment paper.
2. In a medium bowl, whisk together flour, baking powder, baking soda, and salt.
3. In a large bowl, cream together butter and granulated sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla extract and lemon zest.
4. Gradually mix in the dry ingredients to the wet, alternating with sour cream. Begin and end with the dry ingredients.
5. Fold in fresh blueberries and peach slices gently into the batter.
6. Pour batter into prepared pan. Mix brown sugar and cinnamon, then sprinkle over the top.
7. Bake for 45-50 minutes, or until a toothpick inserted into the center comes out clean.
8. Allow to cool in the pan for 10 minutes, then transfer to a wire rack to cool completely.

Notes:

• If using frozen fruits, ensure they are thawed and well-drained to prevent adding excess moisture to the cake.
• For a gluten-free version, substitute all-purpose flour with a gluten-free blend.
• Serve with whipped cream or vanilla ice cream for an extra indulgent dessert.