Heat oven to 200C/180C fan/gas 6 and brush a 12-hole muffin tin with some of the melted butter Put the corn kernels in a pan with the onion, chilli and a knob of butter. Gently fry for 5-10 mins until golden and soft.
Mix together the flour, polenta, baking powder and cheddar with 1 tsp salt in a large mixing bowl. Whisk together the eggs, buttermilk and milk, then stir into the dry ingredients with the remaining melted butter and corn mixture. Divide between the muffin holes (they will be quite full) and bake for 25-30 mins or until golden brown and cooked through - poke in a skewer to check. Best eaten warm.