1. Trim both red and green cabbages, discarding tough outer leaves and core. Slice into 1/4-inch-thick slices. Bring a large stockpot of water to a boil; add 2 teaspoons salt. Cook red cabbage 1 minute. Using a slotted spoon, transfer cabbage to a colander, and drain. Repeat with green cabbage. Pat cabbage dry, and set aside.

2. Melt butter in a large skillet set over medium heat. Add shallot and celery seeds; cook until fragrant, about 2 minutes. Add cream; bring to a boil. Reduce heat; simmer until cream has slightly thickened, about 5 minutes.

3. Add cabbage to skillet, and season with salt and pepper. Cook cabbage until heated through, 3 to 5 minutes. Serve immediately.