Preheat the oven to 400 degrees.
Peel, pit and slice the peaches in to about 1/2" thick wedges. Add to a medium bowl and toss with coconut sugar, cinnamon, nutmeg, lemon, and cornstarch. Transfer to a 1 1/2 quart baking dish or an 8x8 pan also works but will be a bit thicker. Dot with butter.
Bake for 10-12 minutes until the peaches just start to release their juices.
While the peaches bake, make the topping: Add the gluten free flour blend OR all purpose flour to a bowl. Add coconut sugar, baking powder, and salt and stir to combine. Add the butter and cut in with a pastry blender or your hands until the butter is the size of peas.
Add the buttermilk and stir to combine. You should have a dough that clings to the spoon. Don't overmix. If the dough is too dry, you can add an extra tablespoon of milk to bring it together.
When the peaches are ready, bring out the dish and dollop over the batter. Spread it out some with your fingers but don't fuss over it.
Mix the last tablespoon of sugar with the cinnamon and sprinkle over the dough.
Bake until golden and bubbling and the dough is cooked through--about 25 minutes more. Serve warm with ice cream or at room temperature.