In a medium bowl, combine 0.75 cups mayonnaise, 2 tbsp fresh lemon juice, 1 tsp lemon zest, 1 tsp Dijon mustard, 1 tsp white wine vinegar, 1 tbsp extra-virgin olive oil, 0.5 tsp grated garlic, and 0.5 tsp anchovy paste (if using). Whisk until smooth and emulsified. Season with 0.25 tsp freshly ground black pepper and taste for salt — anchovy paste and mayonnaise provide saltiness, so add flaky sea salt only if needed. Refrigerate for at least 15 minutes to allow flavors to meld.

Salad

Prep frisée

Trim any tough stem ends from 6 cups frisée, separate leaves, and spin or pat dry very well. Place the frisée into a large mixing bowl.

Prepare anchovies

Drain 12 anchovy filets from their oil and pat dry on paper towels. Reserve 4 extra anchovy filets for final plating. Finely chop the remaining anchovies into 1/4-inch pieces. In a small bowl, combine the chopped anchovies with the minced shallot and the zest of 1 lemon; gently mix to combine.

Dress the salad

Add 3–4 tablespoons of the prepared lemon mayo to the frisée (start with less — you can add more to reach desired coating). Add the anchovy/shallot/lemon-zest mixture to the bowl. Using clean hands or salad tongs, toss the frisée gently but thoroughly until leaves are evenly coated with lemon mayo and the anchovy bits are distributed. Taste and add flaky sea salt sparingly (about 1/4–1/2 tsp total, adjusting for saltiness from anchovies) and 1 tsp freshly ground black pepper as needed.

Plate and finish

Divide the dressed frisée among 4 plates (approximately 1.5 cups per serving). Arrange the reserved 4 anchovy filets on top (one per plate, or slice each into halves to place two). Drizzle each portion with a light 1/4 tsp (total 1 tsp) extra-virgin olive oil and finish with a small pinch of flaky sea salt and a grind of black pepper. Serve with lemon wedges and toasted crostini on the side so diners can squeeze extra lemon or enjoy with bread.