Place egg whites into Thermomix bowl with cream of tartar.
Whip 4 min/37°C/Butterfly/speed 3 until the egg whites have mounted. Remove carefully from bowl and set aside. Remove Butterfly as well.
Without cleaning the bowl, place yolks, kefir, salt, vanilla paste, caster sugar and baking powder into the Thermomix bowl and blend 10 sec/speed 6.
Add melted butter through hole in lid as you blend 10 sec/speed 4.
Add flour and blend 6 sec/speed 5.
Add half the whipped egg whites to the mixture in the Thermomix bowl and combine 10 sec/speed 5. Add remaining egg whites and fold in carefully. You do not need a completely smooth batter, it should look quite lumpy.
Let the batter rest for at least 30 minutes, covered.
Heat a frying pan to a medium–high heat. The frying pan must be well heated before starting to cook.
Melt a teaspoon of butter for each pancake, and dollop spoonfuls of batter per pancake. Cook on each side until golden.
Serve with all your favourite toppings, though we love plain old butter.