Make the hot honey (if desired): Combine ½ cup honey, 1–2 tablespoons red pepper flakes, and optional ½ teaspoon apple cider vinegar in a small saucepan. Heat gently over low heat for 5–7 minutes until fluid, without boiling. Remove from heat and let steep for 15–20 minutes or longer for more heat. Strain if desired and set aside.

Cook the beef bacon: Cook the beef bacon until crispy. On the stovetop, heat a heavy skillet over medium heat and cook for 8–12 minutes, flipping occasionally. Alternatively, bake at 400°F (200°C) for 15–20 minutes on a lined baking sheet. Drain on paper towels, reserve about 1 tablespoon of rendered fat, and break bacon into 2–3 pieces.

Prepare the fillings: Wash, core, and thinly slice the Granny Smith apple (about 1/8-inch thick). Grate or thinly slice the sharp cheddar cheese.

Assemble the sandwiches: Butter one side of all 8 bread slices. On the unbuttered side of 4 slices, layer half of the cheddar cheese, apple slices, and beef bacon. Drizzle 1 tablespoon of hot honey over each. Top with remaining cheddar cheese and cover with the remaining bread slices, butter-side facing out.

Grill: Heat a heavy skillet over medium-low heat with 1 teaspoon reserved bacon fat or butter. Place sandwiches butter-side down and cook for 4–6 minutes per side, pressing gently, until golden brown and the cheese is fully melted. Cook slowly to avoid burning.

Serve: Transfer sandwiches to a cutting board and rest for 2–3 minutes. Cut diagonally, sprinkle with flaky sea salt or drizzle with more hot honey if desired, and serve warm.