Preheat the oven to 375°F. Have a 9x13-inch pan ready.
In a medium bowl, whisk together the 1 cup oat flour, ¾ cup fine or medium grind cornmeal, 2 teaspoons baking powder, and ½ teaspoon fine sea salt, then stir in the 1 cup whole milk and 3 tablespoons unsalted butter until smooth.
Pit and chop the 2 ½ pounds fresh peaches roughly, then place them in the baking pan and mix them with the 2 tablespoons fresh lemon juice, 2 tablespoons cornstarch or arrowroot, ½ teaspoon ground cinnamon, and 3 tablespoons maple syrup until combined. Spread the mixture out in an even layer in the pan, then evenly pour the batter over the filling.
Place in the oven and bake for about 45 minutes, until the topping is set and golden brown and the fruit is bubbling. Remove from the oven and let cool for about 20 minutes before serving.
Notes
No need to peel the peaches. I don't peel my peaches when I make cobbler, and I’ll leave that decision up to you. I also roughly chopped them, though you could slice them instead.
Adjust the sugar. Change the amount of sugar to taste - use ½ cup if you want the topping to be less sweet.
Use honey. Peaches and honey also go so well together, so try swapping the maple syrup for honey in the filling.
Make it vegan. This recipe is so easy to make vegan, and here's how: Swap the melted butter for melted coconut oil or melted dairy-free butter, and use non-dairy milk for the milk.
Try a different fruit. Any stone fruit would be so good here! If you feel like doing a little work, pit a bunch of cherries and tuck them under the batter. Nectarines make an easy 1:1 swap. Or try a mixture of fruit!
To serve: Peach cobbler would make a wonderful 4th of July dessert; serve it with a big bowl of whipped cream and strawberries alongside. Or, make a colorfully festive version by swapping the peaches for a mix of chopped strawberries and/or raspberries, and blueberries.