To make the pastry, place pistachios into the Thermomix bowl and chop 3 sec/speed 7. Add flour, salt and sugar and combine 5 sec/speed 7. Add butter and combine 10 sec/speed 5 until a course meal forms. Add ice water gradually until dough comes together 10 sec/speed 5. Tip dough out on to a floured silpat mat, flatten into a disc, wrap and refrigerate for 30 minutes.
Preheat oven to 200°C.
Place leek and EVOO into the Thermomix bowl and cook 5 min/Varoma/speed 1. Transfer to a bowl.
Place garlic into the Thermomix bowl and chop 3 sec/speed 6. Add feta, cream, salt and pepper and combine 10 sec/speed 6. Set aside.
Divide dough into 4 pieces. Roll each out to a dinner plate sized circle on it's own piece of baking paper. Spread the cheese mixture onto each piece of pastry, leaving a 1" border. Top with dill, leek mixture and then sliced potatoes. Drizzle generously with EVOO. Place galettes onto oven trays.
Fold edges of dough in, creating a border around the filling.
Bake for 30-35 minutes until crusts are golden brown and potatoes are soft. Garnish with more dill.