For the Bacon-Ranch: In a large cast iron skillet set over medium heat, cook bacon, stirring occasionally, until crisp, 4 to 6 minutes. Using a slotted spoon, transfer bacon to a paper towel–lined plate; reserve drippings.

In a medium bowl, stir together mayonnaise, sour cream, pickle brine, dill, chives, garlic, and black pepper. Fold in cooked bacon and 1 ½ teaspoons of reserved drippings. Cover and refrigerate until ready to use. Wipe skillet clean.

Arrange drained pickle slices on a large paper towel–lined plate; pat dry. In a wide, shallow bowl, combine buttermilk and black pepper. Add pickles, stirring to evenly coat with buttermilk mixture.

Line a 13- by 18-inch rimmed baking sheet with parchment or wax paper; set aside. In another wide, shallow bowl, whisk cornmeal, flour, garlic powder, onion powder, paprika, cayenne, and salt to combine. Working with several pickle slices at a time, toss to evenly coat pickle slices with cornmeal mixture. Place dredged pickles on prepared lined baking sheet.

Line another 13- by 18-inch rimmed baking sheet with paper towels; set aside. Fill the same cast iron skillet with ¾-inch of oil and heat over medium-high until oil registers 375ºF (190ºC) on an instant-read thermometer. Working in batches of about 8, carefully add pickles, sliding them in from as close to the oil’s surface as possible to minimize splashing. Fry pickles, using a spider skimmer or slotted spoon to turn them occasionally, until golden brown and crisp about 1 ½ minutes. Transfer to prepared baking sheet. Season with salt and serve with bacon ranch.