Bring a large pot of water to a rolling boil. Using a knife to draw an X in the bottom of each peach. In batches of 2 or 3, blanch the peaches for 30-60 seconds or until the peach skin begins to pull away from the X slices. Use a slotted spoon to move the peaches into a large bowl of ice water. After they have cooled, peel and chop the peaches, discarding the skin.
In a large skillet, combine chopped peaches, butter, brown sugar and salt over medium heat. Cook for several minutes until the butter and sugar have melted and the peach juices have released and mostly evaporated. Mix together the lemon juice and cornstarch and add it to the peaches.
Whisk together the flour, 2 tablespoons sugar, baking powder and salt. Stir in the cream, butter and vanilla extract with a fork until the dough is just combined. In a small bowl, combine the remaining tablespoon of sugar and cinnamon.
Divide the peaches into 2 5-inch cast iron skillets (note: you can also use one 10-inch skillet, but it may alter the bake time). Use a spoon to evenly distribute the dough over the peaches (it will not completely cover them). Sprinkle the cinnamon sugar mixture on top of the dough.
Bake for 18-22 minutes, or until the sides are bubbly and the dough has cooked through.