Wash cabbage head, cut in quarters, removing stalk
Cook in covered saucepan with 1"  salted water until tender
Drain, reserving water, then press out moisture ( I use a wooden spoon)
Chop and squeeze out more moisture
Make white sauce: Melt butter, add flour and whisk Add milk a little at a time and whisk until smooth Add reserved cabbage water a little at at time until sauce is the right consistency, stirring constantly. You'll want to keep it a little on the thicker side, since the cabbage will give up some moisture Season with salt and pepper to taste
Add cabbage to white sauce, stir to combine
Serve with cinnamon sugar to top ( the traditional Danish way) or salt and pepper. I've also seen some people sprinkle nutmeg or cardamom on top.

Melt butter, add flour and whisk
Add milk a little at a time and whisk until smooth
Add reserved cabbage water a little at at time until sauce is the right consistency, stirring constantly. You'll want to keep it a little on the thicker side, since the cabbage will give up some moisture
Season with salt and pepper to taste