Prepare the dough and confit the night before!
For the dough, combine butter, milk and sugar in a small saucepan and heat until butter is melted. Cool slightly. Meanwhile, in a large baking bowl, using the dough hooks of a mixer, combine flour, yeast, egg, salt and pepper. While stirring constantly with a spoon or the dough hooks, add the warm milk. Continue beating for about 3 min until a soft dough is formed. Form into a clean baking dish and refrigerate with the lid closed for one night.
For the confit, in a heavy saucepan over moderate heat, melt the butter with the Íl. Add the shallots or onions and garlic if needed and saute for about 40 to 60 min until the onions are very soft. season with salt, cool and put in the fridge with the lid closed.
In the morning, preheat the oven to 190 °C. Lightly oil a baking tray. Place the dough on a lightly floured surface and divide into three pieces. Roll out each piece into a round slab 3 mm thick.
Spread each slab with one-third of the confit. Cut each slab into quarters.
Roll up the dough quarters from the base so that the opposite corner is on top. Place, this side down, on a greased baking sheet. When all croissants are formed, rest 15 min.
In a small bowl, whisk together egg yolks and water and generously brush the tops of the croissants with the mixture. Place in zi