Chocolate-Hazelnut Fudge

Preheat oven to 350 degrees. Place hazelnuts in a single layer on a rimmed baking sheet; toast until golden and fragrant, about 14 minutes.

Lightly brush a standard 9-by-5-inch loaf pan with butter; line in both directions with parchment. Melt 1 1/2 cups dark chocolate in a medium bowl set over a saucepan of simmering water. Brush loaf pan all over with half of melted chocolate; freeze 5 minutes. Brush again with remaining melted chocolate and freeze 5 minutes more.

In a medium bowl set over a saucepan of simmering water, melt remaining 1 1/2 cups dark chocolate with milk chocolate, stirring together until smooth. Remove from heat; stir in hazelnut spread and hazelnuts. Pour into chilled chocolate shell and refrigerate until firm, at least 4 hours. Trim chocolate around top of loaf pan with a paring knife. Let temper 30 minutes before slicing crosswise into 8 pieces. Torrone can be refrigerated, covered, up to 2 weeks.