1. Cut top and bottom off 1 lemon; cut into 8 to ten 1/4-inch-thick slices. Cut remaining lemon into 8 wedges and set aside. Arrange lemon slices in single layer across bottom of 12-inch skillet. Scatter dill stems and 2 tablespoons minced shallots evenly over lemon slices. Add wine and water.

2. Place salmon fillets in skillet, skinned-side down, on top of lemon slices. Set pan over high heat and bring liquid to simmer. Reduce heat to low, cover, and cook until sides are opaque but center of thickest part is still translucent (or until instant-read thermometer inserted in thickest part registers 125°F), 11 to 16 minutes. Remove pan from heat, and using spatula, carefully transfer salmon and lemon slices to paper towel-lined plate and tent loosely with foil.

3. Return pan to high heat and simmer cooking liquid until slightly thickened and reduced to 2 tablespoons, 4 to 5 minutes. Strain cooking liquid through fine-mesh strainer into medium bowl; discard solids. Return strained liquid to skillet; whisk in Dijon mustard and remaining 2 tablespoons shallot. Simmer over high heat until slightly thickened and reduced to 2 tablespoons, 4 to 5 minutes. Whisk in sour cream and juice from 1 reserved lemon wedge; simmer 1 minute. Remove from heat; whisk in 2 tablespoons unsalted butter and 2 tablespoons minced fresh dill fronds. Season with salt and pepper.

4. Season salmon lightly with salt and pepper. Using spatula, carefully lift and tilt salmon fillets to remove lemon slices. Place salmon on serving platter or individual plates and spoon sauce over top. Serve, passing reserved lemon wedges separately.

Serves 4