Place chestnuts in a small saucepan with 3 tbsp of water over medium-low heat. Cook for 5 minutes, stirring occasionally, until warmed through and slightly softened.

Transfer warm chestnuts to a food processor. Add honey, softened butter, cinnamon, and salt. Blend until smooth and paste-like, scraping down the sides as needed.

Taste and adjust honey if needed. Transfer filling to a bowl, press plastic wrap directly onto the surface, and refrigerate for 30 minutes until firm enough to shape.

Combine flour, powdered sugar, and salt in a large mixing bowl. Add cold butter cubes and rub together with your fingertips until the mixture resembles coarse breadcrumbs.

Add egg yolk and cold milk. Mix with a fork, then knead briefly just until the dough comes together into a smooth ball. Do not overwork it.

Flatten the dough into a disc, wrap in plastic wrap, and refrigerate for 30 minutes.

Heat the oven to 180 C / 355 F. Line a sheet pan with parchment paper.

Divide the chilled dough into 18 equal portions, about 15 g each. Roll each piece into a ball, then flatten into a disc about 5 cm wide.

Divide the chestnut filling into 18 portions, about 10 g each. Roll each portion into a small ball.

Place a filling ball in the center of a dough disc. Bring the edges up around the filling and pinch firmly to seal, then roll gently between your palms to form a smooth oval.

Use the back of a fork to press ridges along the length of each pastry, mimicking a chestnut shape. Place on the prepared tray, spaced 2 cm apart.

Refrigerate the shaped pastries on the tray for 15 minutes while the oven finishes preheating.

Whisk egg yolk with milk to make the egg wash. Brush each pastry lightly with egg wash using a pastry brush.

Bake for 18 to 20 minutes until the shells are light golden brown on top and slightly deeper on the base.

Remove from the oven and cool on the tray for 10 minutes before transferring. The shells will firm up as they cool.