Preheat oven to 425°F.
Melt 1/2 Tbsp butter in a 10-inch cast-iron skillet over medium-high.
Add peach and jalapeños; cook, stirring, approx 3 minutes. Jalapenos will be tender and peaches will start to caramelize.
While the peaches and jalapeno are cooking, in a large bowl, whisk cornmeal, flour, baking powder, baking soda and salt.
In a small bowl, whisk milk, lemon juice, and eggs.
Add milk mixture to the cornmeal mixture; stir until combined. It will be a bit runny. It shouldn't be thick.
Stir in peach and jalapeno mixture.
Put the empty skillet to the preheated oven for 5 minutes. During this time, allow the cornmeal mixture to rest.
Carefully remove skillet from oven. Remember the handle will be HOT.
Add 1 Tbsp butter to the skillet, swirl it around to coat the skillet.
Pour cornmeal/peach batter into skillet.
Bake 18-20 minutes or until golden brown and center is cooked thoroughly.