Smoky cubes of brined city ham and salty bits of country ham give this main-course mac its name and savory appeal. Pasta enrobed with a creamy sauce and melting pockets of gooey cheese take it over the top.
Preheat oven to 350°. Prepare pasta according to package directions for al dente.
Stir together smoked ham and country ham. Sauté half of ham mixture in 1 Tbsp. hot oil in a large skillet 7 to 8 minutes or until lightly browned. Repeat with remaining ham mixture and oil.
Melt 6 Tbsp. butter in a large saucepan over medium heat. Add onion and next 5 ingredients, and sauté 30 seconds or until fragrant. Add flour, and cook, stirring constantly, 2 minutes or until golden brown and smooth. Gradually whisk in milk and cream, and bring to a boil, whisking occasionally. Reduce heat to medium-low, and simmer, whisking constantly, 5 minutes or until slightly thickened and mixture coats a spoon. Stir in horseradish and Worcestershire sauce. Remove from heat, and stir in Cheddar cheese until melted. Stir in pasta, ham, and Gruyère; pour into a lightly greased 13- x 9-inch baking dish.
Process breadcrumbs and 2 Tbsp. melted butter in a food processor 6 to 7 seconds to combine. Sprinkle over pasta mixture.
Bake on an aluminum foil-lined jelly-roll pan at 350° for 30 minutes or until bubbly and golden. Remove from oven to a wire rack, and cool 15 minutes. Top with chives.
Note: We tested with Cracker Barrel Extra Sharp Cheddar.