Trim pork belly to square off its edges. Rinse the pork, pat it dry, and transfer it to large sheet of parchment paper.
Measure out salt, sugar, black peppercorns, fennel seed, caraway seed, rosemary, thyme, and bay leaves and coarsely grind in a spice grinder. In a bowl, combine garlic with spices and set aside.
Rub seasonings all over pork. Transfer pork and any excess spices to a 1-gallon resealable plastic bag and seal, shaking the bag to distribute the seasonings. Refrigerate for 7 days on a sheet tray, flipping the bag every other day. (Some brine will accumulate in the bag as the salt draws water from the pork.)
After 7 days, the bacon should feel firm to the touch. Remove bacon from the bag and thoroughly wash off the spices under cold running water. Pat bacon dry with paper towels.
Heat oven to 200°. Transfer bacon to a 9 x 13 baking pan and roast until meat is lightly browned and an instant-read thermometer inserted in the center reads 150°, about 2 hours.
Transfer bacon to a cutting board. With a long, thin knife, slice off the skin. Let bacon cool to room temperature. Pat bacon dry, wrap in wax paper, and refrigerate until completely chilled. Wrap bacon in plastic wrap and refrigerate for up to 10 days or freeze for up to 3 months. Slice and fry up for the breakfast table or cut into lardons for a salad.