1. Preheat oven to 350°. Sprinkle 1 1/3 cups toasted pecans into 2 well-buttered shiny 9-inch round cake pans; shake to coat bottom and sides of pans.
2. Stir together flour and next 3 ingredients.
3. Stir together eggs and next 4 ingredients in a large bowl until blended. Add flour mixture, stirring just until blended. Fold in apples, carrots, and remaining 1 cup pecans. Pour batter into prepared pans.
4. Bake at 350° for 30 to 35 minutes or until a wooden pick inserted in center comes out clean. Cool in pans on wire racks 10 minutes. Remove from pans to wire racks, and cool completely (about 1 hour).
5. Place 1 cake layer, pecan side down, on a serving plate. Spread top of cake layer with 2/3 cup Apple Cider Caramel Sauce; top with remaining cake layer, pecan side down. Spread Mascarpone Frosting over top of cake. Drizzle 2 Tbsp. Apple Cider Caramel Sauce over frosting, and swirl sauce into frosting. Serve immediately.