Pistachio paste
Shell the pistachios by plunging them in boiling water for 2 minutes.
Drain the pistachios and place them in a kitchen towel. Close the towel and massage to remove as much skin as possible.
Recover the pistachios that have no skin and remove the skin with your fingers for the pistachios that still have it.

Preheat the oven to 300 F (150 C).
Spread the pistachios in a single layer on a non-stick baking sheet and bake for 10 minutes, until they are slightly colored.
Bring the water and sugar to a boil, until the temperature reaches 250 F (121 C).
Pour the syrup over the pistachios and mix.
Let cool, then transfer to a food processor with the almond flour and bitter almond extract.
Process in pulses until you obtain a pistachio powder.
Continue to process, stopping from time to time to avoid overheating the mixture. Scrape the sides with a spatula.
When the mixture starts to pale, add the oil and continue to pulse until the mixture is smooth.
Store in the refrigerator in an airtight container.

Chocolate and pistachio biscuits: Cream the butter with the sugars and pistachio paste.
Incorporate the egg, mixing well, then add the flour.
Melt the chocolate in a double boiler and pour it into the dough.
Incorporate the shelled pistachios.

Cover the bowl with plastic wrap and refrigerate for at least 1 hour.

Preheat the oven to 350 F (180 C) and prepare 2 baking sheets lined with parchment paper.
Scoop out the biscuit dough with a spoon and shape into balls the size of a golf ball.
Place them on the baking sheets, flattening them slightly and leaving a space of 2 inches (5 cm) between them.
Bake for 10 minutes.
The biscuits should still be soft when they come out of the oven; they will harden as they cool.