2. Melt the butter in a large saucepan over medium heat, add the onions and garlic and cook, stirring occasionally, until the onions are translucent but not colored, 6 to 7 minutes. Add the sauerkraut, cover with the wine and 1 cup water and heat just to a boil.
3. Wrap the juniper berries, coriander seeds, and bay leaves in a cheesecloth, add this sack to the sauerkraut, lower the heat to low, cover, and simmer for 45 minutes. Bury the slab bacon under the sauerkraut, cover, and simmer for an additional 45 minutes.
4. Cook the potatoes in boiling salted water until soft, about 20 minutes, and then drain.
5. Fill the bottom of a steamer about halfway with water, add the vinegar, and heat to a boil. Season the salmon fillets with salt and pepper, place in the steamer basket, top with the fresh thyme, cover, and steam until just cooked through, 5 to 6 minutes.
6. To serve, spoon a mound of sauerkraut in the center of four plates, top each with a salmon fillet and a slice of slab bacon, surround with potatoes, and serve with coarse sea salt alongside.