Fill a large pot with lightly salted water and bring it to a boil.
Add the bow tie pasta to the boiling water and cook for 8 to 10 minutes, stirring occasionally, until tender.
Drain the pasta in a colander and set aside.
Melt the butter in a large saucepan over medium heat.
Add the minced garlic to the melted butter and cook for about 30 seconds until fragrant.
Whisk the flour, salt, and black pepper into the butter mixture.
Cook the flour mixture for 1 to 2 minutes, stirring constantly, until smooth.
Slowly whisk in the milk, a little at a time, until fully combined.
Bring the milk mixture to a boil and cook for 1 minute.
Stir in the shredded Colby cheese and mustard.
Cook the sauce, stirring occasionally, until the cheese melts completely.
Remove the saucepan from the heat.
Add the cooked pasta, julienned ham, and frozen peas to the cheese sauce and stir to combine.
Pour the pasta mixture into a 2-quart baking dish.
Sprinkle the grated Parmesan cheese evenly over the top.
Bake for 20 to 25 minutes until bubbly and golden.
Notes
Tips and Tricks
Don't Overcook the Pasta - Cook the pasta just until tender since it will continue cooking in the oven. Overcooked pasta can become mushy in the final dish.Whisk Constantly - When making the cheese sauce, whisk continuously to prevent lumps from forming. This creates a smooth, creamy texture.Add Milk Slowly - Pour the milk into the flour mixture a little at a time while whisking. This helps the sauce thicken evenly without clumps.Let It Rest - Allow the casserole to sit for 5 minutes after baking. This helps the sauce set up and makes serving easier.Use Room Temperature Cheese - Shredded cheese melts more evenly when it's not cold from the fridge. Let it sit out for 15 minutes before using.
Storing and Reheating
Refrigerate - Store leftovers in an airtight container in the refrigerator for up to 4 days.Freeze - Freeze the casserole in a freezer-safe container for up to 3 months. Thaw overnight in the refrigerator before reheating.Reheat in Oven - Cover the casserole with foil and reheat at 350 degrees F for 15 to 20 minutes until warmed through.Reheat in Microwave - Place a serving in a microwave-safe dish and heat on medium power for 1 to 2 minutes, stirring halfway through.