Slow-Simmered Caramelized Onion Soup

By AislePrompt Editorial · Published 2026-04-23 · Updated 2026-04-23

A deeply sweet and savory soup made with onions cooked low and slow until golden brown, finished with a touch of thyme and crusty bread. This French-inspired soup recipe (vegetarian), ready in about 85 minutes, pairs yellow onions, unsalted butter, all-purpose flour for a weeknight-friendly dinner that comes together with one pan and minimal cleanup. Each serving lands at about 310 calories and feeds 6, so it slots cleanly into a weekly meal plan and pairs well with a quick salad or grain on the side. Tap "Plan a meal with the AI" below to drop this recipe into your week and send the ingredients straight to Instacart. Nutrition values are approximate, calculated from USDA FoodData Central (fdc.nal.usda.gov) — verify against ingredient labels for any health-driven dietary plan.

Ingredients

• 1 lb, thinly sliced yellow onions
• 3 tbsp unsalted butter
• 1 tbsp all-purpose flour
• 3 cups chicken stock
• 1 tsp, chopped fresh thyme
• 4, toasted baguette slices

The stock pot we’d simmer this in → Best Stock Pots for 2026: Top Picks + Buying Guide

Instructions

1. Step 1: Melt 3 tbsp unsalted butter in a large Dutch oven over medium-low heat, then add 1 lb thinly sliced yellow onions, stirring to coat.
2. Step 2: Cook onions for 45 minutes, stirring every 5 minutes, until deeply caramelized and golden brown, reducing heat if browning too quickly.
3. Step 3: Sprinkle 1 tbsp all-purpose flour over onions and stir for 1 minute to cook off raw flour taste.
4. Step 4: Gradually whisk in 3 cups chicken stock, bring to a gentle simmer, then stir in 1 tsp chopped fresh thyme and cook uncovered for 15 minutes.
5. Step 5: Ladle soup into bowls over toasted baguette slices, garnishing with extra thyme if desired.