Set your Instant Pot to sauté mode and melt 4 tablespoons of unsalted butter. Add the sliced yellow onions, stirring frequently for about 15 minutes until they soften and turn deep golden brown.

Once the onions are nicely caramelized, sprinkle in ½ teaspoon each of salt and pepper along with ½ teaspoon of dried thyme. Stir in the 2 tablespoons of flour.

Pour in ½ cup of dry red wine and continue sautéing for another 1-2 minutes.

Add 6 cups of beef broth to the pot, stirring well. Seal the lid and set to high pressure for 5 minutes.

After the timer goes off, perform a quick release of the pressure. Open the lid and give the soup a gentle stir.

Slice your baguette into ½-inch thick rounds and grate ¾ cup of Gruyere cheese. Preheat your oven to broil on high.

Ladle the soup into oven-safe bowls, place a slice of baguette on top, and sprinkle with grated Gruyere cheese. Broil for 2-3 minutes until the cheese is bubbly and golden.