Melt the butter in a cast iron skillet over medium high heat. Place the cabbage wedges in the skillet, cut side down. Cook until charred (approx. 2-3 minutes), flip and char the other side. Lower the heat to medium low and use tongs to remove the cabbage from the skillet.
Add the onion, garlic & a healthy pinch of pepper to the empty skillet and cook down for 2 minutes - if the skillet is too dry add a tiny bit of oil.
Pour in the milk, cream, mozzarella and bouillon. Mix until the cheese has melted and the sauce has thickened slightly. Add the spinach and lemon juice and mix to combine. Taste and adjust the seasonings if needed. Turn the heat off.
Add the cabbage back to the skillet and spoon some sauce over the wedges. Carefully cover with foil and place in the oven (on the center rack) for 30 minutes.
Remove from the oven, top with chives and serve.
Video
Notes
Cut a whole cabbage in half (cutting through the stem so the halves stays intact). Then quarter the half, again, keeping the stem intact.
If you don't have a cast iron skillet you could also use a dutch oven.
My favorite vegan creamers for savory dishes are Trader Joe's Heavy Whipping Cream or Ripple Creamer.