Rinse konbu under running water. Transfer konbu to a medium saucepan and add 8 cups water. Bring water to a simmer over medium heat. Turn off stove and let stand for 10 minutes.
Remove konbu from saucepan and add bacon. Bring to a boil over medium-high heat, then reduce heat to a gentle simmer. Simmer bacon for 30 minutes.
Remove bacon from saucepan. Transfer liquid to an airtight container and chill until fat separates and hardens on top. Remove fat and discard. Store dashi covered and refrigerated, up to 3 days.