Melt the butter in a large pot over medium heat until it starts to foam. Add the finely chopped onion and minced garlic, stirring gently. Cook for about 3–4 minutes, or until the onions turn soft and slightly golden, releasing their sweet aroma.

Sprinkle in the flour, stirring continuously to form a smooth, golden paste. Allow this roux to cook for 1–2 minutes to eliminate the raw taste of the flour.

Slowly pour in the chicken or vegetable broth, a little at a time, whisking vigorously to avoid any lumps. Bring the mixture to a gentle boil, then reduce the heat to a low simmer.

Gradually add the heavy cream, stirring until fully incorporated. Let the soup simmer for about 5 minutes, allowing it to thicken into a velvety base.

Crumble the blue cheese into the pot, reserving some for garnishing. Stir gently as the cheese melts, enriching the soup with its creamy texture and bold flavor. Taste the soup and adjust the seasoning with salt and freshly cracked pepper, keeping in mind the saltiness of the cheese.

If a silky smooth texture is desired, use an immersion blender to puree the soup until it reaches a consistent and creamy finish.

Serve the soup warm, ladling it into bowls and garnishing with the reserved blue cheese crumbles and fresh parsley for a vibrant touch. Pair with crusty bread or savory crackers to complete the meal.