In a 10-in. cast-iron skillet, melt 2 tablespoons butter; tilt to coat bottom and sides. Add the onion, jalapeno and 1/4 teaspoon chili powder; cook over medium-low heat until onion is lightly browned and tender. Stir in 1 tablespoon brown sugar until dissolved; set aside.
In a large bowl, combine the flour, cornmeal, sugar, baking powder, salt, baking soda, and remaining chili powder and brown sugar. In a small bowl, whisk the buttermilk, eggs and melted butter. Stir into dry ingredients just until moistened. Fold in cheese and chiles.
Pour over onion mixture in skillet. Bake at 425° for 20-25 minutes or until golden brown. Meanwhile, in a small saucepan, cook cranberry sauce and lime zest over low heat until heated through. Cool completely.
Let cornbread stand for 10 minutes. Invert onto a serving platter; cut into wedges. Pour cranberry mixture over softened butter; serve with cornbread.
Wear disposable gloves when cutting hot peppers; the oils can burn skin. Avoid touching your face.