Preheat the oven to 375 F
Butter a 9-inch square baker (should be large enough so apples do not touch). Using a paring knife or apple corer, cut three-fourths of the way into each apple making a one inch wide opening. Make 5 1-inch slits around the opening of the apple to prevent the skin from exploding.
Spoon a teaspoon of sugar into each hole, followed by a teaspoon of hazelnuts, and then raisins. Top with 1/2 tablespoon of butter in each apple hole and a drizzle of sweet wine. Pour a little sweet wine in the baking dish, reserving 2 tablespoons for the mascarpone.
Bake for about 45 minutes or until a paring knife easily pierces the apple. Add extra wine or water if the liquid evaporates on the bottom of the baking dish.
While the apples bake, in a small bowl mix the mascarpone, 2 tablespoons of the sweet wine, honey, and vanilla.
To serve, cut each apple in half, drizzle any pan juices over the apple and a dollop of the mascarpone sauce.