Combine warm water, yeast, and sugar in a small bowl. Let it sit until the yeast becomes foamy, approximately 5 minutes. This proves your yeast is active and ready for the Gipfeli Recipe. Meanwhile, place flour in a large mixing bowl.

In another bowl, mix warm milk, sugar, and salt until dissolved. Blend the milk mixture, yeast mixture, and oil into the flour. Mix well until smooth and no dry flour remains. Cover the bowl and let it rise until it triples in size, about 3 hours.

Gently press down the risen dough to release air bubbles. Cover again and let rise until doubled in size, approximately 3 hours. This second rise develops flavor and improves texture.

Press dough down gently and chill for 20 minutes. Meanwhile, knead the cold butter until pliable but still cold. Roll the chilled dough into a 14×8-inch rectangle on a floured surface.

Spread butter evenly over the top two-thirds of the dough rectangle, leaving a 1/4-inch margin around edges. Fold the unbuttered third over the middle third, then fold the buttered top over that, creating three layers.

Rotate the dough 90 degrees so the folds are positioned left and right. Roll into a rectangle again. Fold in three layers as before. Sprinkle lightly with flour and refrigerate in a plastic bag for 2 hours.

Unwrap dough and sprinkle with flour. Gently deflate and roll flat into a rectangle. Fold again into thirds, turn 90 degrees, and repeat the folding process. Chill for another 2 hours. Preheat oven to 475°F (245°C).

Shape dough into a 20×5-inch rectangle. Chill half while working with the other half. Roll out to a 15×5-inch rectangle. Cut into three 5×5-inch squares, then slice each square diagonally in half.

Gently roll each triangle to elongate to 7 inches long. Stretch the other 2 points as you roll it up from the wide end to the tip. Arrange on parchment-lined baking sheets, slightly curved. Let rise until puffy, about 30-45 minutes.

Mix egg and water for egg wash. Brush each croissant with egg wash for golden color. Bake until golden brown and flaky, approximately 12-15 minutes. Cool on wire racks before serving.