Preheat oven to 250°. Mix jam, red pepper flakes, and vinegar in a small bowl; season with salt. Set half of spicy fig jam aside.
Spread 6 slices of bread with remaining spicy fig jam and top with cheddar and remaining 6 slices of bread. Spread outside of sandwiches with butter.
Heat a large skillet over medium heat. Working in 2 batches, cook sandwiches, pressing down firmly, until golden brown and cheese is melted, about 1 minute per side. Transfer to a wire rack set inside a baking sheet and keep warm in oven until ready to serve. Cut each sandwich into 4 triangles and serve with reserved spicy fig jam for dipping.
Mothers Secret Recipes of Comfort Food & Culinary Inspiration from an Organic and Allergen-free Approach