Very coarsely grind the coffee using a pestle and mortar or food processor. (Espresso or pre ground coffee will not strain out with your average sieve, so coffee beans are a must here!)
Select Sauté on the Instant Pot and set the time to 3 minutes.
Add the double cream, sugar and coffee, and sauté until warm. (Do not let it boil.)
Whisk the eggs, then gently stream the coffee cream into the yolks, whisking constantly to prevent the eggs scrambling.
Add the coffee liquor, then pour the whole mixture into a large dish, and set it aside to infuse for a minimum of 45 minutes.
After 45 minutes, pour the coffee cream through a sieve (you can line the sieve with muslin for an extra smooth finish) and discard the coffee grounds.
Divide the coffee cream between 6 heat safe jars (we used 120ml), filling them to about 80% full. Close the jar lids, enough to stop moisture, but not too tight as air needs to release during cooking.
Clean the inner pot from excess cream, then place the trivet inside. Fill the pot 1/5 of the way up with warm water.
Select Sous Vide, set the temperature to 83°C and the timer to 1 hour. Once the water is at the correct temperature, lower in the jars, making sure the water line is just below the jar lids. Sous vide the custards until just set. Start checking the custards around 30 minutes. To know they are set, give them a tap and they should wobble slightly.
Once cooked, place in the fridge to set and cool for 2-3 hours.
When ready to serve, whip the 125ml cream to soft peaks and spoon over the custards.