Preheat your oven to 350°F (175°C) and grease a 9-inch round cake pan.

In a medium bowl, whisk together the all-purpose flour, baking powder, ground cinnamon, and salt.

Cream the softened unsalted butter and packed brown sugar together until light and fluffy, about 3-5 minutes.

Add the room temperature eggs one at a time, mixing well after each addition, then stir in the vanilla extract.

Gradually add the dry flour mixture to the wet ingredients, alternating with the whole milk, mixing until just combined.

Gently fold in the diced fresh peaches, ensuring they are evenly distributed, then pour the batter into the prepared cake pan.

Bake for 40-45 minutes, or until a toothpick inserted into the center comes out clean. The top should be golden brown.

Allow the cake to cool in the pan for about 10 minutes before turning it out onto a wire rack to cool completely.