Preheat the oven to 375 F.
Bring a large pot of water to a rolling boil.
Blanch the peaches to removethe skin. (See Tips and Tricks below recipe!)
Set peaches aside to cool.
Meanwhile, in the bowl of a stand mixture fitted with a paddle attachment, combine the sugar and butter until well blended.
Add the eggs one by one.
Next, add the yolk. Continue to beat until it the batter comes together.
Add the flour and baking powder and mix until combined.
Remove the tart shell from the refrigerator. Dock the bottom ( See Tips and Tricks below!)
Smooth the cake batter into the bottom of the 9-inch tart evenly.
Cut the peaches in half and remove the pit.
Cut each peach half in half again.
Press each peach half, cut side down, into the cake batter, starting at the perimeter of the of the tart crust.
Continue to use all the peaches, placing in a circular fashion.
Bake in the oven on the lowest rack for about 20 minutes.
Sprinkle the peaches with the remaining sugar.
Bake an additional 10-15 minutes, until the peaches begin to caramelize.