Preheat your oven to 400°F (200°C).

Slice the head of garlic in half and place the halves cut-side up on a baking tray. Drizzle with olive oil and roast for 30 to 40 minutes until golden brown and soft.

While the garlic is roasting, pour the chicken stock into a large pot and bring it to a gentle boil. Add salt and dried sage, reduce heat to low and simmer.

Once the garlic is roasted, let it cool slightly and mash it into a smooth paste.

In a bowl, whisk the egg yolk and Dijon mustard together. Gradually add olive oil in a steady stream while whisking to create an emulsion.

Add the mashed garlic into the simmering chicken stock and stir well. Slowly add the egg yolk and olive oil emulsion while whisking continuously.

Ladle the soup into bowls and serve with roasted baguette slices for dipping.