Step 1

Preheat oven to 425°. Peel and finely chop 4 garlic cloves. Cut 2 whole heads of garlic in half crosswise. Strip leaves off 1 rosemary sprig, discard stem, and finely chop leaves. Finely chop 1 Tbsp. fennel seeds.

Step 2

Mix chopped garlic, chopped rosemary, chopped fennel seeds, salt, and 1 Tbsp. oil in a small bowl; season with pepper.

Step 3

Rub garlic mixture all over 1½ lb. pork tenderloin on a rimmed baking sheet (if you have time to do this in the morning, great; chill pork until dinner).

Step 4

Scatter remaining 4 rosemary sprigs in a large baking dish and set tenderloin on top. Wrap 4 bacon slices around tenderloin, tucking ends underneath so bacon stays put.

Step 5

Nestle halved heads of garlic around tenderloin and drizzle with remaining 1 Tbsp. oil.

Step 6

Roast until an instant-read thermometer inserted into thickest part of tenderloin registers 145° for medium, 30–40 minutes. Transfer to a cutting board and let rest at least 10 minutes before slicing.

Step 7

Do Ahead: Pork can be rubbed with garlic mixture 1 day ahead. Cover and chill.