In a small bowl, whisk together mayonnaise, ketchup, sweet pickle relish, smoked paprika, garlic powder, salt and black pepper until creamy. Cover and refrigerate for dipping sauce.

Layer 6 flour tortillas with Swiss cheese slices, corned beef, optional sauerkraut, and another slice of Swiss cheese on top. Place remaining tortillas over and press gently.

In a skillet, heat grapeseed oil over medium-high heat until shimmering. Adjust heat if oil starts smoking.

Cook quesadillas for about 2-3 minutes until golden brown on one side, then flip and cook another 2-3 minutes until cheese melts and quesadillas are golden brown.

Let cooked quesadillas rest on a cutting board, then cut into wedges and serve with the chilled dipping sauce.