Bacon Deviled Eggs

Place 12 large eggs in a large saucepan; add water to cover by 1". Bring to a boil, cover, and remove from heat. Let sit for 10 minutes. Drain. Transfer eggs to a bowl of ice water and let cool completely, about 10 minutes; peel. Halve lengthwise and remove yolks. Coarsely chop 3 slices of bacon. Cook in a medium skillet over medium heat until browned and crisp. Transfer bacon to paper towels. Strain drippings through a fine-mesh sieve into a small bowl. Add melted butter if needed to measure 2 tablespoons. Finely mash reserved yolks, bacon fat (and/or butter), 1/3 cup mayonnaise, 2 teaspoons Dijon mustard, and 1 heaping tablespoon chopped scallions in a medium bowl; season with kosher salt and freshly ground black pepper. Transfer to a large resealable freezer bag, then cut 1/2" off 1 corner. Pipe into whites; garnish with thinly sliced scallions and reserved bacon.