For the cornichon dressing: In a medium bowl, mix together the mayonnaise, cornichons, Dijon mustard, mustard powder, tarragon and lemon juice. Season with salt and pepper.
For the shrimp fritters: Heat about 1 1/2 inches vegetable oil in a heavy-bottomed pot until a deep-fry thermometer inserted in the oil registers 350 degrees F.
In a small mixing bowl, whip the egg whites to medium peaks; set aside. In a separate bowl, combine the shrimp, scallions, zucchini, garlic and jalapenos and set aside.
Whisk together the flour, baking powder and paprika in a medium bowl. Whisk in the egg yolks and enough of the buttermilk so the mixture is thick and not runny (adjust the amount accordingly). Season with salt and pepper. Fold the shrimp mixture into the batter, followed by the egg whites just to incorporate.
Drop the fritters into the oil in batches using a small scoop or spoon, about 1 tablespoon each. Cook until golden brown, about 5 minutes, then drain on paper towels. Immediately season with salt. Serve with the cornichon dressing.