In a large mixing bowl, combine the all-purpose flour, granulated sugar, and active dry yeast. Create a well in the center and pour in the whole milk and one egg. Stir with a wooden spoon until a sticky dough forms, then knead on a floured surface for 5–10 minutes until it’s smooth and elastic.

Shape the kneaded dough into a ball and place it in a lightly oiled bowl. Cover the bowl with a damp cloth or plastic wrap, and let it rise in a warm area for about 1 hour, or until it doubles in size.

Transfer the risen dough to a floured surface and roll it into a rectangle about 1/4 inch thick. Spread softened unsalted butter over two-thirds of the dough, then fold the unbuttered third over the middle section. Fold the remaining third over that, creating layers. Roll the dough out again and repeat the buttering and folding process one more time.

Now, roll the dough out to about 1/2 inch thick. Use a sharp knife or pizza cutter to cut the dough into squares, around 4 inches on each side. Place a tablespoon of your desired filling in the center of each square, then fold the corners of the dough over to create a pocket, sealing the edges well.

Arrange the filled cruffins upright in a greased muffin tin. Cover them lightly with a kitchen towel and let them rise for about 30 minutes, or until they puff up noticeably.

Preheat your oven to 375°F (190°C). Once the cruffins have risen, bake them for 20–25 minutes until golden brown.