Heat the oven to 450 degrees F.
In a 10-inch cast iron pan on medium-high heat add the bacon and saute until almost crisp then add the onions and season with a pinch of salt and a couple of grinds of pepper. Saute until the onions are tender, then add the garlic and stir. When the garlic is tender use a slotted spoon to remove the mixture to a medium bowl and set aside. Leave the bacon fat in the cast iron pan and keep it on medium heat while you make the batter.
In a large bowl combine the cornmeal, baking powder, baking soda and salt. Stir the buttermilk, eggs, butter, and chiles into the bowl with the bacon mixture. Make a well in the center of the dry ingredients and gently pour in the egg mixture. Fold until all the ingredients are combined. Immediately pour the batter into the cast iron pan. Transfer the pan to the oven and bake until golden brown on top and a toothpick inserted in the center comes out clean, about 30 minutes.
Glaze: Melt the butter, sugar and a pinch of salt together in a small pan over low heat, stirring to dissolve the sugar. Once the cornbread is done, remove it from the oven and immediately pour the glaze over the top. Slice and serve warm.