Whisk together sugar and condensed milk with warm milk. Add yeast and an egg, then whisk again.
Combine wet and dry ingredients, including flour and salt.
Work the dough until it comes together using dough hooks. Add the butter and knead the dough for ten minutes.
Allow the dough to rest for one hour.
⅔ of the dough is divided and rolled into a 25×40 centimeter rectangle.
The dough is rolled into a log and then cut into pieces. Place dough pieces in a preheated baking dish and set aside.
To make smaller buns, repeat the procedure with the remaining 1/3 of the dough.
Allow the rolls to rest for one hour.
Before baking, brush the top of each bun with egg wash.
Bake at 180C/350F for twenty-five to thirty minutes. For smaller buns, twenty minutes will suffice.
Butter and condensed milk are whisked in equal proportions. Apply this mixture to warm buns while they are still warm.
When completely cooled, remove the baked goods from the baking pans.