Preheat oven to 400°F (200°C). Toss together sweet potato rounds, olive oil and 1/3 of each salt and pepper. Arrange in single layer on baking sheet; bake for about 10 minutes or until tender.
Reduce oven to 350°F (180°C). Grease baking dish; set aside.
Melt butter in saucepan set over medium heat; add sage leaves. Cook for about 5 minutes or until ends begin to curl and butter is browned but not scorched. Transfer sage leaves to paper towel–lined plate.
Stir rice flour into butter in saucepan; cook for 2 minutes. Whisk in whipping cream, a splash at a time, until smooth. Cook, stirring constantly, for 5 to 7 minutes or until thickened. Remove from heat. Stir in remaining salt and pepper, Parmesan and nutmeg.
Ladle 1/5 of sauce into bottom of prepared dish. Top with one-third of the lasagne noodles, breaking noodles to fit snuggly. Top with 1/5 of sauce, 4 sage leaves, 1/3 of mozzarella, 1/3 of hazelnuts and 1/3 of the sweet potato slices. Repeat layers twice. Top with remaining sauce and sage leaves.
Place heart-shaped cookie cutter in centre of lasagne and fill with crumbled amaretto cookies.
Cover with foil; bake for 45 minutes. Remove foil; bake for about 15 minutes or until noodles are tender and sauce is bubbling. Let stand for 10 minutes before serving.