Place bacon in freezer for 10 minutes to firm up. (Partially freezing the bacon keeps the fat from stocking to blade or grinder.) Coarsely chop and pulse in food processor to grind or push through the meat grinder attachment for a stand mixer.
Season beef with a little Kosher salt and more black pepper then add bacon and combine well. Form 4 patties thinner at center for even cooking.
Preheat a griddle or cast-iron skillet over medium to medium-high heat.
Stir up the sauce ingredients in a small bowl: blue cheese, sour cream, horseradish, chives and Worcestershire.
Cook patties 3-4 minutes, pressing with a spatula for even browning and a good crust. Flip and cook 5 minutes more, again pressing occasionally to make a good crust.
Stack burgers: bun bottoms, lettuce, white onion, pickles, burger, blue cheese-horseradish sauce and bun tops.
Serve with oven fries or good quality ruffled chips and peeled baby carrots and celery sticks alongside.