Preheat your oven to 400°F (200°C). Slice the top off the garlic bulb, exposing the cloves, and place it on a baking tray. Drizzle with olive oil until well coated, then roast for 30–40 minutes.

While the garlic is roasting, grab a large pot and pour in the chicken stock. Bring it to a gentle boil over medium heat, then add the dried sage along with a pinch of salt. Once boiling, reduce the heat to low and let it simmer for about 10 minutes.

After the garlic has roasted, squeeze the soft cloves out of their skins into a mixing bowl. Mash the roasted garlic into a smooth paste with a fork.

In a separate bowl, whisk together the egg yolk and Dijon mustard until smooth. Gradually drizzle in the olive oil while whisking vigorously to create an emulsion.

Fold the mashed garlic paste into your simmering broth, whisk to blend well, and heat on low for another 5 minutes, ensuring it doesn't boil.

Ladle the soup into warm bowls and serve, ideally with crusty bread on the side.