In the bowl of your food processor, combine flour, baking powder and salt and blitz quickly. Add the cubed butter and pulse until coarse crumbs form. In a small bowl, stir together eggs, oil and water and add to the dry mix. Pulse until the dough comes together in clumps. Take out and knead very quickly. Divide the dough into 4 parts, shape it into individual disks, wrap in cling film and let rest in the fridge for about an hour, better for 2.  You can prepare the dough 2 days ahead of time. 

Preheat the oven to 375 F, or 180 C . Line 2 large baking sheets with parchment paper. Let dough sit on the counter for about 5 minutes, so that it is easier to roll.  In the meantime, blend all the ingredients except for the chocolate in your food processor until a coarse, thick paste forms. If it is too dry, add some more espresso or rum. It should hold together when squeezed between your fingers. Stir in the chocolate.

Roll out dough on a lightly floured surface until 3 mm thin.Cut out rounds of about 8 to 10 cm. 

Place about a teaspoon of the filling on the lower half of each round. Moisten the edge of the round with water, then fold the round in half and seal the edges with a fork or your fingers. Place the chestnut cookies on the baking sheets.

Bake for 15 to 18 minutes or until just starting to brown.Transfer them to a bowl filled with the confectioner's sugar as soon as they come out of the oven. Roll them in the icing sugar and let cool on wire racks. The chestnut cookies should be stored in airtight containers in a cold room. Properly stored, they keep for at least 2 weeks.