In a large bowl or stand mixer bowl, combine flour (500g), sugar (60g), salt (10g), and instant yeast (9g). Whisk to distribute evenly.

Add the cold milk (250g) and egg (1). Mix until a shaggy dough forms. It will look rough—that's fine.

Add the softened butter (40g). Knead until the dough is smooth, elastic, and slightly tacky but not sticky. About 5-7 minutes by mixer or 8-10 minutes by hand.

Shape dough into a rectangle roughly 8x6 inches. Wrap tightly in plastic wrap. Refrigerate at least 4 hours or overnight.

Place cold butter chunks (250g) and flour (15g) into the mixer bowl. Fit with the paddle attachment. Mix on LOW speed only, just until flour is fully incorporated and butter is smooth and cohesive. About 30-60 seconds.

Place butter and flour in a bowl. Press and fold together using a spatula, scraper, or your hands. Work quickly to keep butter cold.

Place butter on parchment paper. Shape into a 6 x 6 inch (15 x 15 cm) square. Wrap tightly in parchment. Refrigerate until cold, firm, and flexible (not rock hard).

Remove dough and butter block from fridge. Leave both wrapped on counter for 15-30 minutes. The butter should be cold but flexible—it should bend without cracking or feeling soft.

Roll chilled dough into a 10 x 10 inch (25 x 25 cm) square. Place butter block diagonally (diamond shape) in the center. Fold dough corners over butter to fully enclose and seal. Press gently to secure.

Roll dough into an 8 x 20 inch (20 x 50 cm) rectangle. Fold both short ends toward the center. Fold closed like a book. Wrap and refrigerate 30 minutes.

Roll again into an 8 x 20 inch (20 x 50 cm) rectangle. Fold into thirds like a letter. Wrap and refrigerate 30-60 minutes.

After the final chill, roll dough to 1/4 inch (6mm) thickness. The dough should be about 12 x 16 inches.

Using a sharp knife or pizza cutter, trim the edges for clean cuts. This exposes the layers and ensures even puff.

Cut into 4 x 4 inch (10 x 10 cm) squares. You should get 8-12 pieces depending on your roll.

For each square: Cut from each corner toward the center, stopping 1/2 inch from the middle. Fold alternating corners toward the center, pressing gently to secure.

Place 1-2 tablespoons of filling in the center of each shaped pastry. Do not overfill—excess filling will bubble over and burn.

Place shaped pastries on parchment-lined baking sheets, spaced 2 inches apart. They will expand during proofing and baking.

Drape plastic wrap loosely over the pastries, or use a large inverted sheet pan. The covering prevents drying but shouldn't touch the pastries.

Let rise for 1 1/2 to 2 hours until slightly puffy and relaxed. The dough should look pillowy but NOT doubled in size.

The pastries are ready when they jiggle slightly when the pan is moved and the layers look distinct. If the butter starts to look greasy, they've proofed too long or the room is too warm.

Starting from each corner, cut diagonally toward the center, stopping about 1/2 inch from the middle.

Take every other corner point and fold it toward the center, pressing gently to secure. You'll have 4 points meeting in the middle.

Place a dollop of filling in the center where the points meet. Press gently to nestle it into place.

Place 1-2 tablespoons of filling in the center of the square.

Bring all four corners to the center, overlapping slightly. Press firmly to seal.

Press the center where the corners meet to ensure they stay closed during proofing and baking.

Preheat your oven to 375°F (190°C) for at least 20 minutes. A fully preheated oven is essential for proper puff.

Beat the egg with milk or cream. Brush each pastry lightly, avoiding drips that could glue them to the parchment.

Bake for 18-22 minutes until deeply golden with visible layers. The layers should be distinct and the tops should look dry, not doughy.

For extra shine, brush with simple syrup (equal parts sugar and water, heated until dissolved) immediately after removing from the oven.

Let cool on the pan for 5 minutes, then transfer to a wire rack. These are best eaten within a few hours while the layers are still crisp.