Step 1

In a small bowl, combine the butter and the chopped thyme, mixing to incorporate the herbs. If you like, spoon the herb butter into the center of a piece of parchment or wax paper and roll it into a log shape. Chill the butter for at least an hour for easy slicing. If you don't want to make the butter log, just chill the butter in a bowl covered with plastic (it won't look as good, but the butter is going to melt in the oven anyway).

Step 2

Preheat the oven to 425°F (220°C).

Step 3

Melt the remaining 2 tablespoons of the butter in a large pan, and saute the cabbage and scallions over medium heat until tender, about 6 minutes. Portion the cooked cabbage into 6 equal piles in a casserole dish.

Step 4

Place a halibut fillet on each pile of cabbage, season with salt and pepper, and drizzle with lemon juice and white wine. Cut the prepared herb butter into 6 equal-sized pats, and place one on top of each fillet. Scatter halved tomatoes evenly around the fillets. Top each piece of halibut with 2 sprigs of thyme. Cover the casserole with foil and bake for 20 minutes.