Put the canola oil in a 9 or 10 inch cast iron skillet and place the skillet in the oven. Heat oven to 400°F with the skillet inside.
In a large bowl, whisk together the cornmeal, flour, baking soda and salt.
In a separate bowl, whisk together the yogurt, milk, and egg.
Pour the wet ingredients into the bowl of dry ingredients and stir to combine. Stir in melted butter, jalapeños, corn & cheese.
Once the oven has reached 400°F and the skillet is hot, carefully remove the empty skillet from the oven (the handle is hot!). Pour the cornbread batter into the skillet, and smooth the surface.
Return the skillet to the oven and bake for ~20 mins, until lightly browned on top and a skewer inserted comes out clean.
Let the jalapeño cornbread rest in the skillet for at least 10 mins before cutting wedges and serving. Remember that the skillet is still very hot.