Preparation

• Mix the mascarpone, dill, 1 tsp. lemon zest, and 2 tsp. lemon juice in a medium bowl. Season with salt, pepper, and more lemon juice or zest to taste. Using a sharp vegetable peeler, peel the fennel into long, thin strips by pressing firmly against it; season the strips with salt.
• To assemble, spread the toasts with some of the mascarpone and then cut each toast into four even squares. Top each square with a couple of pieces of the fennel, a curl of the salmon, a dill frond, and a few grinds of black pepper.

Make Ahead Tips

You can make the mascarpone spread and prep the fennel several hours in advance. Keep both refrigerated; bring to room temperature before assembling.