Mac&Cheese With Peas and Bacon

1 lb. elbow macaroni
kosher salt
3 TBSP. unsalted butter
3 TBSP. all-purpose flour
4 C. warm whole milk
5 1/2 C. shredded sharp white cheddar cheese
freshly ground black pepper
extra-virgin olive oil
4 slices bacon, cut crosswise into thin strips
1 lg. onion, diced
2 garlic cloves, minced
leaves from 1/4 bunch fresh thyme
2 C. frozen peas, thawed in a colander under cool water

Bring a pot of salted water to a boil over high heat. Add 1 lb. elbow macaroni and cook until al dente, about 8 to 9 minutes, and drain. Preheat oven to 400º. Melt 3 TBSP. unsalted butter in a large deep skillet over medium-high heat. Whisk in 3 TBSP. all-purpose flour and cook for about 1 minute, stirring constantly to keep lumps from forming. Gradually whisk in 4 cups warm whole milk. Whisk vigorously, and continue to cook until the mixture is thick and smooth. Stir in 4 cups shredded sharp white cheddar cheese and continue stirring until the cheese is melted. Season the cheese sauce with salt and pepper, then add cooked macaroni to the pan. Mix well until macaroni is fully coated with the cheese mixture.
Scrape contents of pan into a 3-quart baking dish and sprinkle the top with 1 1/2 cups shredded sharp cheddar cheese. Bake for 30 minutes, or until hot and bubbly.
As the mac & cheese is baking, heat a 2-count of olive oil in a saute pan. Add 4 slices of bacon, cut crosswise into thin strips, 1 lg onion (diced), 2 garlic cloves (minced), and leaves from 1/4 bunch fresh thyme and cook for about 5 minutes, until onion is softened.
Fold in 2 cups frozen peas (thawed under cool water), and season with salt and pepper.
Remove mac & cheese from the oven. Scatter the top of the mac & cheese with the pea and bacon mixture and serve.