Remove the peel from the garlic and squeeze (or pound in a mortar) into a large enough bowl. Add the yolks, mix with an electric whisk and then, with the machine running, add the olive oil, first drop by drop, then in a thin stream, until the mixture is creamy. Now season with cayenne pepper (hot!) and salt.
Add a few saffron threads if desired.
Cut baguette into slices and toast lightly in the hot stove. Spread with the garlic mayonnaise and bring to the table warm.