Mostarda

• 2 1/2 cups seedless red grapes (from 2 medium bunches)
• 1/2 cup granulated sugar
• 1/2 cup red wine vinegar (such as California Cabernet)
• 2 tablespoons yellow mustard seeds
• 2 teaspoons Aleppo pepper
• 1/2 teaspoon fine sea salt

Panini

• 4 (1/2-inch-thick) sourdough bread slices
• 2 aged white cheddar cheese slices (about 1 1/2 ounces)
• 1 ounce crumbled blue cheese (such as Roquefort)
• 4 prosciutto slices (about 2 ounces)
• 2 tablespoons unsalted butter, softened