1. Preheat oven to 400°.
2. To prepare cakes, place cauliflower, potato, and shallots on a baking sheet. Drizzle 1 1/2 tablespoons oil over vegetables; toss. Bake at 400° for 35 minutes or until tender, stirring once. Place cauliflower mixture in a food processor; pulse 10 times or until chopped. Scrape mixture into a bowl. Add fontina, thyme, salt, 1/2 teaspoon pepper, and egg, stirring well.
3. Combine panko and Parmigiano-Reggiano in a shallow dish. Using wet hands, shape cauliflower mixture into 8 (1-inch-thick) patties; dredge in panko mixture. Place patties on baking sheet. Bake at 400° for 25 minutes or until browned, turning once.
4. To prepare sauce, combine sour cream and next 5 ingredients (through garlic) in a small bowl.
5. To prepare salad, combine arugula, tomatoes, 2 teaspoons oil, and juice; toss well to coat. Place 1 cup arugula mixture on each of 4 plates; top with 2 cakes and 1 tablespoon herb sauce.