Macaroni and Cheese with Kielbasa and Mustard | America's Test Kitchen

Ingredients

• 6 slices white sandwich bread (good-quality, about 6 ounces), torn into rough pieces
• 3 tablespoons unsalted butter (cold), cut into 6 pieces
• 1 pound elbow macaroni
• 1 tablespoon table salt
• 5 tablespoons unsalted butter
• 1 medium onion, chopped fine
• 6 tablespoons all-purpose flour
• 8 ounces smoked kielbasa, cut lengthwise into quarters, then cut crosswise into 1/2 inch slices
• 1 1/2 teaspoons powdered mustard
• 1/4 teaspoon cayenne pepper (optional)
• 5 cups milk (see note)
• 8 ounces Monterey Jack cheese, shredded (2 cups)
• 8 ounces sharp cheddar cheese, shredded (2 cups)
• 4 teaspoons whole-grain Dijon mustard
• 1/2 teaspoon table salt