SHRIMP & CRAB SWEET POTATO SLIDERS      PREP + COOK TIME 35 MINUTES MAKES 12  The sweet potatoes need to be about 2¾ inches in diameter, as they will serve as the "buns" for the sliders.    3 purple-skinned white-fleshed sweet potatoes, unpeeled  ¼ cup olive oil  12 large shrimp (10 ounces), peeled, deveined, with tails intact  2 cups watercress sprigs  ¼ cup fresh micro sorrel leaves  ¼ cup fresh cilantro leaves  1 tablespoon extra-virgin olive oil  1 tablespoon lemon juice  1 medium avocado    crab filling  6½ ounces cooked crab meat  ½ cup crème fraîche  ½ clove garlic, crushed  1 green onion (scallions), chopped finely  1 tablespoon finely chopped fresh chives  1 tablespoon nigella seeds  2 tablespoons horseradish cream  1 tablespoon lemon juice      1 Cut eight ½-inch-thick rounds from each sweet potato (you need 24 rounds in total); discard tapered ends. Brush rounds with 2 tablespoons of the olive oil; season. Cook rounds, in batches, on a heated grill pan (or barbecue) for 6 minutes each side or until cooked through. Remove from heat; keep warm.    2 Make crab filling.    3 Coat shrimp in remaining olive oil; season. Cook shrimp on heated grill pan for 1 minute each side or until just cooked through. Remove from heat; cover to keep warm.    4 Place watercress, sorrel, and cilantro in a small bowl with extra-virgin olive oil and juice. Season; toss to combine. Mash avocado in a small bowl.    5 Place 12 sweet potato rounds on a board; top each with crab filling, a shrimp, mashed avocado, and watercress salad. Top with remaining sweet potato rounds.    crab filling Combine ingredients in a small bowl; season.    nutritional count per slider 13g total fat (3.2g saturated fat); 216 cal; 15.1g carbohydrate; 8.4g protein; 3g fiber    tip We used crème fraîche in the crab filling rather than a commercial aïoli or mayonnaise, as they tend to contain refined sugars unless made from scratch.   Excerpted from Sugar Free by tbd, Australian Women's Weekly Test Kitchen Staff All rights reserved by the original copyright owners. Excerpts are provided for display purposes only and may not be reproduced, reprinted or distributed without the written permission of the publisher.