
Preheat oven to 425℉.
Slice cabbage into 8 wedges keeping core intact.
Add butter and oil to a 12" skillet, and place over heat to melt butter. Remove from heat.
Add cabbage wedges and arrange to fit in the skillet.
Sprinkle with a good pinch of salt and pepper.
Flip them over and salt and pepper again.
Add the onion slices, pushing them into the crevices to get coated with the oil and butter.
Roast for 60 minutes, flipping halfway through.
Meanwhile, add the honey and crushed red pepper into a small pan. Heat and bring just to a simmer then remove from heat.
Stir in the mustard and vinegar.