To prepare the day before: In the bowl of a stand mixer, combine flour, salt, and sugar.
Add beaten eggs and yeast diluted in milk.

Knead for 10 minutes with the dough hook.
Cut the butter into small pieces and add them, a few at a time, while continuing to knead.
Kneading may take 15 minutes, until the butter is well incorporated.
The dough will be heavy and soft.

Cover the mixing bowl with plastic wrap and let the dough rise for 2 hours at room temperature, then refrigerate overnight.

The next day: Place the dough on a floured work surface.
Cut the dough into 4 equal parts.
Roll out each part into a rectangle of 1/4 inch (0.5 cm) thickness.
Sprinkle each rectangle with milk chocolate and white chocolate chips.
Roll each rectangle into a roll, starting from the long side and pressing tightly to form a roll.
Using a knife, cut the roll in half lengthwise.
Twist the two pieces, making sure the cuts are always on top.
Seal the ends by tucking them under, then place the twist on a baking sheet lined with parchment paper.
Repeat the steps with the remaining 3 pieces of dough.

Cover the twists with a clean cloth and let them rise for 1 hour 30 minutes.

Preheat the oven to 350 F (180 C).
Beat the egg and milk, then brush the twists with the mixture.
Bake the twists for 30 to 35 minutes, or until they are golden brown.
Remove from the oven and let cool on a wire rack.