Very lightly adapted from Russ Parsons's How to Read a French Fry. (And he says he got the crisp-skinned trick from Thomas Keller.) Parsons adds a touch of cumin seeds to the leeks and cabbage; I prefer it without, but if you are always pro-cumin, add a half-teaspoon of the seeds along with the leeks. —Nicholas Day
Trim the leeks, leaving only the white and pale green parts. Slice lengthwise into quarters and rinse well, until any sand and mud are gone. Thinly slice crosswise.
Cut the cabbage into quarters, remove the tough core, and thinly slice. Slice the bacon into thin strips.
In a large skillet, cook the bacon and 2 tablespoons of the butter over medium-high heat until the bacon is crisp, about 5 minutes. Reduce the heat to medium, add the leeks and cook for another 5 minutes or so, until the leeks soften. Add half the cabbage and cook, stirring, for another 10 minutes, or until the cabbage softens. Add half of the remaining cabbage (not all of it) and cook for another ten minutes, until that softens.
Meanwhile, squeegee the salmon: Rub the back of a knife across the skin of the salmon, not cutting it, but firmly rubbing it, until moisture collects on the knife. Wipe dry the knife and the salmon and repeat, until moisture no longer forms. Cut the salmon into four pieces and season with salt on both sides.
Add the remaining cabbage to the leeks and cabbage, along with the cream. Stir and cook until any liquid is no longer visible when the pan is tilted. Salt to taste. Add the last two tablespoons of butter to the pan and cook for another minute, just until the sauce thickens. Keep warm.
While the cabbage is finishing, heat the oil in a large skillet over high heat. When the oil is hot, add the fillets skin side down and cook until the skin is very crisp and the flesh is lightened only about one-third of the way up the side, about 2 to 3 minutes. Then turn the fillets and remove the pan from the stove; it will finish cooking off the heat while you serve the leeks and cabbage. Then serve the salmon immediately.