On a smooth and clean surface place the flour, add the salt, sugar, yeast and in the center pour the cold water. Incorporate the ingredients into a smooth dough, if you are using an stand mixer knead at minimum speed for 5 minutes.

Add butter. Work the dough until the butter is completely incorporated. If using an an stand mixer knead at second speed for 15 minutes.

Transfer the dough to a plastic container sprinkled with flour. Cover with a plastic film and let fermenate for 90 minutes.

Sprinkle flour over the already fermented dough and press with your hands to deflate dough.

Make balls about 2”(5cm) in diameter and arrange in a deep rectangular pan leaving 2”(5cm) space between them.

Cover with a damp cloth and move the pan to a place free of wind at a temperature of approximately 80F (27C). You can also keep the pan inside the oven turned off with a glass of hot water inside, that will create humidity to ferment and grow the buns.

Wait until the dough doubles in volume (about 30 minutes).

Preheat the oven to 375F (180C). To create moisture place 500 ml of water inside the oven, make sure that the container is heat proof.

Crack an egg in a glass and with a fork stir quickly to mix white and yolk. Brush the buns with the beaten egg.

Bring the buns to preheated oven and bake for about 30 minutes until golden.

Remove from oven and allow to cool completely before removing from baking sheet.

Serve warm.