Use the flat beater with your stand mixer bowl to whisk together almond, butter, icing sugar and salt at low speed. Once homogeneous, add the eggs one by one. Don't worry if there are still lumps. They will disappear once we add flour. Add the flour little by little. The dough should NOT be smooth, it should still be clumpy. Remove from the bowl and finish smoothing it out by hand. The reason why we are doing this? We want to make sure that we don't overknead our dough. Lots of bakers have trouble with their pie dough retracting when they bake it. It's actually because gluten activates and becomes elastic. If you knead the dough for too long (even with the flat beater!), it can retract during baking. Cover your dough and let it rest for at least 2 hours in the fridge.