Roast Beef Panini

Ingredients

• 1/4 cup mayonnaise
• 2 teaspoons sun-dried tomatoes, minced
• 1 teaspoon garlic, minced
• 1 teaspoon prepared horseradish
• 1 teaspoon ketchup
• 1 pinch cayenne pepper
• 1/3 cup red onion, slivered
• 1/3 cup pickled sweet peppers (I used a mixture of hot and sweet)
• 1 pinch red pepper flakes
• 4 slices sourdough bread, 1/2 inch thick
• butter, softened
• 1/2 cup white cheddar cheese, shredded
• 4 ounces deli roast beef, thinly sliced