Heat the oven to 425°F and line a large plate with a paper towel. Set aside.
Add the bacon to a 12-inch cast iron skillet over medium heat. Cook until the bacon is brown and crisp, about 3 minutes per side. Remove the bacon -- but not the bacon fat -- from the skillet. Set the bacon aside on the paper towel-lined plate.
Add the onion to the bacon fat in the skillet and cook over medium-low heat for about 4 minutes. Add the jalapeños and sauté until the mixture is aromatic and the onions are soft, about 2 more minutes. Crumble or finely chop the bacon and add it to this mixture, along with the corn. Now add the butter to the skillet, swirl it around the bottom and sides to melt it into the other ingredients. Season to taste with salt and pepper. Turn off the heat and leave the skillet as it is on the stove.
In a large mixing bowl, stir the cornmeal, baking soda, salt, sugar and cumin. In another large bowl, whisk the eggs, buttermilk and lemon juice together. Then stir the wet ingredients into the dry and mix until smooth.
Slowly pour the batter into the skillet and mix until everything is totally incorporated. You'll want to be sure you don't see any "pools' of the melted butter. Place the skillet in the 425°F preheated oven. Bake until the edges are golden and it no longer jiggles, about 30 to 35 minutes.
Let it cool for at least 20 minutes before serving. Serve directly from the skillet.