Ingredients

• 2 shallots, thinly sliced into rounds
• 1/4 cup apple cider vinegar
• 1/4 cup white wine vinegar
• 1/4 cup sugar
• 1 tablespoon olive oil
• 1 medium red onion, thinly sliced
• Kosher salt
• 1/2 cup red wine
• 1/4 cup red wine vinegar
• 1 tablespoon sugar
• 1/4 cinnamon stick
• 1/2 star anise pod
• 1/8 teaspoon crushed red pepper flakes
• 1/8 teaspoon ground allspice
• 1/4 cup olive oil
• 4 large white onions, thinly sliced
• 1 leek, white and pale-green parts only, thinly sliced
• 2 celery stalks, chopped
• 4 garlic cloves
• 1 serrano chile, seeded, chopped
• 2 tablespoons chopped peeled ginger
• Kosher salt
• 1/2 cup dry white wine
• 1/2 cup mirin
• 1 cup heavy cream
• 2 tablespoons unsalted butter
• 2 slices brioche, quartered
• 4 ounces Fontina cheese, grated
• 1 tablespoon chopped fresh chives

Instructions

1. Place shallots in a small nonreactive bowl. Bring vinegars, sugar, and 1 cup water to a boil in a small saucepan, stirring to dissolve sugar. Pour over shallots; chill.
2. DO AHEAD: Shallots can be pickled 5 days ahead. Cover and keep chilled.
3. For red onion jam: Heat oil in a medium skillet over medium-high heat. Add onion, season with salt, and cook, stirring often, until soft, 5-7 minutes. Add wine, vinegar, sugar, cinnamon, star anise, red pepper flakes, and allspice. Bring to a boil, reduce heat, and simmer, stirring occasionally, until liquid is thickened and syrupy, 40-45 minutes. DO AHEAD: Jam can be made 5 days ahead. Cover and chill.
4. Heat oil in a medium skillet over medium-high heat. Add onion, season with salt, and cook, stirring often, until soft, 5-7 minutes. Add wine, vinegar, sugar, cinnamon, star anise, red pepper flakes, and allspice. Bring to a boil, reduce heat, and simmer, stirring occasionally, until liquid is thickened and syrupy, 40-45 minutes.
5. DO AHEAD: Jam can be made 5 days ahead. Cover and chill.
6. For white onion soup: Heat oil in a large pot over medium-high heat. Add onions, leek, celery, garlic, chile, and ginger; season with salt. Cook, stirring often, until soft (do not let brown), 10-12 minutes. Add wine and mirin to pot, bring to a boil, and cook until reduced by half, about 4 minutes. Reduce heat to medium, cover, and cook, stirring occasionally, until onions are soft and translucent, 25-30 minutes. Let cool slightly, then purée in a blender until smooth. Strain into a large bowl and stir in cream (thin with water, if needed); season with salt. Reheat soup in a clean pot. DO AHEAD: Soup can be made 2 days ahead. Let cool; cover and chill.
7. Heat oil in a large pot over medium-high heat. Add onions, leek, celery, garlic, chile, and ginger; season with salt. Cook, stirring often, until soft (do not let brown), 10-12 minutes.
8. Add wine and mirin to pot, bring to a boil, and cook until reduced by half, about 4 minutes. Reduce heat to medium, cover, and cook, stirring occasionally, until onions are soft and translucent, 25-30 minutes. Let cool slightly, then purée in a blender until smooth. Strain into a large bowl and stir in cream (thin with water, if needed); season with salt. Reheat soup in a clean pot.
9. DO AHEAD: Soup can be made 2 days ahead. Let cool; cover and chill.
10. For fontina toast and assembly: Heat butter in a large skillet over medium heat. Cook bread until golden, about 3 minutes (you'll have 2 extra). Flip, top with cheese, cover, and cook until cheese is melted, about 4 minutes. Top toasts with pickled shallots and chives. Spoon some jam into each bowl, pour soup around, and top with toasts.
11. Heat butter in a large skillet over medium heat. Cook bread until golden, about 3 minutes (you'll have 2 extra). Flip, top with cheese, cover, and cook until cheese is melted, about 4 minutes. Top toasts with pickled shallots and chives.
12. Spoon some jam into each bowl, pour soup around, and top with toasts.