In a large pot or Dutch oven over medium heat, melt butter; add shallots and cook, stirring, until soft but not browned. Mix in tarragon.
Add potatoes. Sprinkle with salt and pepper. Add broth and bring to a boil over medium-high heat. Cover, reduce heat to medium, and boil gently 15 minutes.
Add salmon steaks in a single layer; cover with lemon slices, then add bay leaf. Pour in wine. Cover again and cook over low heat until salmon flakes when tested with a fork and potatoes are tender (10 to 12 minutes). Meanwhile, in a medium skillet, cook bacon in its own drippings until lightly browned. Remove from heat, drain on paper towel, and keep warm.
Remove and discard bay leaf and lemon slices. Remove salmon steaks; discard salmon bones and skin and divide salmon into chunks. Add cabbage and cream to soup. Stir occasionally over medium heat until cabbage is wilted and bright green (3 to 5 minutes). Gently mix in salmon. Taste, and add salt if needed.
Serve chowder hot, spooning several pieces of bacon into each bowl.
Servings: 4 to 6