Knead in the mixer or by hand for 5 minutes, stopping as soon as the dough feels soft and holds. Khapli atta dough tears rather than stretches smoothly, so don't push for a full windowpane test. A slow-rebounding poke test is the better sign of readiness.

Flatten the dough on a lined baking sheet, cover, and refrigerate for 30 minutes.

Roll the chilled dough into a 14×10-inch rectangle, working gently to avoid tearing. Cover and refrigerate for at least 4 hours, or overnight.

Beat the butter and khapli atta or flour together until smooth, spread into a 7×10-inch rectangle on a lined sheet, and chill for 30 minutes until firm but still pliable.

Place the butter layer in the centre of the dough and fold the dough over it to enclose it completely. On a lightly floured counter, roll gently into a 10×20-inch rectangle, then fold lengthwise into thirds like a letter.

If the dough feels warm or resistant, chill for 30 minutes before continuing. Roll into a 10×20-inch rectangle and fold into thirds again for the second turn. Chill 30 minutes, then repeat once more for the third turn.

Cover the folded dough and refrigerate for at least 4 hours, or overnight.

Roll the dough into an 8×20-inch rectangle. Cut in half vertically, then into 3 even horizontal slices to make eight 4×5-inch rectangles, then cut each in half lengthwise for 16 smaller rectangles. Gently stretch each to about 8 inches, place a few pieces of chocolate at one end, and roll up tightly with the seam underneath.

Rest the shaped croissants at room temperature for 1 hour, then refrigerate for another hour (or up to 12).

Preheat the oven to 200°C. Whisk the egg and milk and brush over each croissant. Bake for about 20 minutes until golden, rotating the pans halfway through. Reduce to 190°C if they're browning too quickly.

Cool on a wire rack for a few minutes, then dust with confectioners' sugar if desired.