Preheat the oven to 350F.
In an 8x8 baking pan, create a parchment paper sling.
In a medium mixing bowl, whisk together the flour, baking powder, and salt, and set aside.
In a large mixing bowl using a whisk, beat the butter until light and creamy.
Add the sugar and whisk until light and fluffy, for about 2 minutes.
Add the eggs one at a time, scraping down the bowl and whisking well after each addition.
Whisk in the vanilla and then the sour cream.
Using a wooden spoon, gradually add the flour mixture just until combined.
Fold in three-quarters of the peaches and spread the batter into the prepared baking pan.
Arrange the remaining peaches on top.
Bake for 45 minutes or until a wooden pick inserted into the center comes out clean.
Let cool for at least 30 minutes before serving and remove from the baking pan using the parchment paper sling. Plate and sprinkle with confectioners' sugar if desired.