Preheat the oven to 350°F. Lightly grease a 9x5-inch loaf pan. Set aside.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon, and salt. Set aside.
In a large mixing bowl, beat the softened butter, brown sugar, and granulated sugar together until the mixture is light and fluffy with a stand up mixer or hand held mixer.
Mix in the egg, vanilla extract, and sour cream until fully combined.
Add the dry ingredients to the wet mixture and stir gently until just combined—do not over mix. Over mixing can result in a dense or tough bread.
Gently stir in the diced peaches by hand until evenly distributed throughout the batter.
Spoon the batter into the prepared pan, filling it about halfway full.
In a small bowl, combine the brown sugar, granulated sugar, cinnamon, melted butter, and flour. Stir until the mixture becomes crumbly. Evenly sprinkle the streusel over the batter in the pan.
Bake for 50-55 minutes, or until a toothpick inserted into the center comes out clean.
Remove from the oven and allow the bread to cool fully in the pan before glazing.
Make the glaze. In a small bowl, whisk together the powdered sugar, heavy cream, and vanilla until smooth.
Remove the bread from the pan. Drizzle the glaze over the cooled bread. Slice and serve.