Preparing the Dough:

1. Warm the milk slightly (do not overheat). Mix with yeast and sugar in a small bowl. Let it sit for 5-10 minutes until foamy.
2. In a large mixing bowl, combine flour and salt. Add the cold butter cubes and rub them into the flour with your fingers until the mixture resembles coarse breadcrumbs.
3. Slowly pour in the yeast mixture, stirring to combine. Knead the dough for about 8-10 minutes until smooth and elastic.
4. Cover the dough and let it rest in a warm place for 1 hour, or until it doubles in size.

Shaping the Gipfeli:

1. Roll the dough into a large rectangle (about ¼ inch thick) on a lightly floured surface.
2. Cut the dough into long triangles with a base of about 4 inches.
3. If adding fillings, place a small spoonful of jam, chocolate, cheese, or ham at the base of each triangle.
4. Roll each triangle from the base to the tip, forming a crescent shape.
5. Place the shaped Gipfeli on a parchment-lined baking sheet, ensuring enough space between each piece.

Baking the Gipfeli:

1. Preheat the oven to 375°F (190°C).
2. Beat the egg and brush a light layer over each Gipfeli for a golden finish.
3. Bake for 15-20 minutes, or until golden brown and crisp.
4. Remove from the oven and let them cool slightly before serving.