Different types of oats to use?

Totally agree with AJ. That said, you could also precook the steel cut oats for 5 minutes as she suggests and then put all the ingredients (except the reserved nuts as she recommended) into the prepared baking pan, cover it, and refrigerate it overnight. Take it out in the morning while you're heating your oven, sprinkle the nuts on top, and bake it as directed. (If it's still cold, it might take a little longer.)

Steel cut oats take a lot longer to cook than regular oats, and also require a lot more liquid. To adapt this recipe, I would increase the total amount of milk to 4 cups, but I would jumpstart the steel cut oats by cooking them in 3 cups of milk in the microwave or on the stove for about 5 minutes. I’d then let that sit for about 10 minutes before combining with all of the other ingredients in step 1.

This recipe relies somewhat on the texture of the oatmeal to give it a good top crust, so I would reserve some of the nuts to sprinkle over the whole top of the dish before baking. ;o)