Meanwhile, in a large, deep skillet, cook the bacon over moderately high heat until crisp, about 6 minutes. Drain the bacon on paper towels. Add the butter to the skillet and cook over moderately high heat until browned and nutty, about 3 minutes. Add the Brussels sprouts and hazelnuts and cook until heated through, about 2 minutes. Add the orecchiette along with the reduced chicken stock and simmer, stirring, until the sauce is slightly absorbed, about 2 minutes. Stir in 1/2 cup of the Parmigiano cheese, season with salt and pepper and transfer to a large serving bowl. Garnish with the bacon and the remaining 1/2 cup of cheese and serve.