Patty Melt Sandwich

Ingredients

• 1 lb. ground beef
• ½ tsp. kosher salt
• ¼ tsp. pepper
• 6 tbsp. butter, softened, divided
• 1 lg. onion, sliced
• 6 slices rye bread
• 6 slices sharp cheddar cheese
• Chips and a pickle for serving
• 1 c. mayo
• 1 tbsp. finely chopped onion
• ¼ c. ketchup or chili sauce
• 4 tsp. prepared horseradish
• 1 tsp. hot sauce
• 1 tsp. Worcestershire sauce
• ¼ tsp. smoked paprika
• Salt and pepper to taste