Place Gruyere, Cheddar and spring onions into Thermomix bowl and mill for 5 sec/speed 8. Remove from bowl and set aside.
Place buckwheat into Thermomix bowl and mill for 10 sec/speed 10. Add yeast, water, oil & salt and mix for 6 sec/speed 6. Warm for 2 min/37ºC/speed 2.
Add flour, and seeds and knead for 1 min/Interval.
Add walnuts through hole in lid and knead a further 30 sec/Interval.
Turn out onto floured silicone mat and knead by hand into a tight ball. Wrap and allow to double in size in draft free room. It will be quite a stiff dough.
Roll dough out to a large rectangle and spread generously with crème fraîche. Arrange salami slices evenly, top with milled cheese mixture and olives. Roll carefully into a sausage shape and gently cut into rounds, so as not to flatten the scrolls.
Place cut side up into a large baking dish, cover and allow to prove for around 30minutes. Place into cold oven set to fan forced 200ºC (to allow a further rise) and bake for 25-35 minutes or until golden and sounding hollow when tapped.