These really are a great breakfast to make and are easily scaled up or down depending on how many guests you have! Don't have cast iron skillets? No problem, use shallow ramekins (like for creme brulee) or even deeper ones (just adjust the cooking time). Or, do it in a full-sized skillet with lots of eggs! There's no wrong way to make these! Don't like parmesan - try cheddar...or goat cheese...or swiss...but if you're going to use parm, avoid the grated kind that comes in a green jar since it doesn't really melt. Oh, and don't skip the cream as that helps to keep everything moist and prevents the yolks from drying out.
*A note on cooking time. We like soft cooked yolks, so for us, 4-5 minutes is perfect. Cook them longer for yolks that are more set. At 6 minutes, they'll still be liquid but will be on the verge of being hard cooked. We suggest checking them sooner than later as you can always pop them back in a little longer.