Place peanuts onto a tray and into a cold oven set to 200°C for 15 minutes. Remove and cool, then roughly chop. Set aside. Turn oven down to 180°C.
Line a loaf tin with paper that comes up on two sides for easy removal.
Place peanut butter, butter, sugars, salt and vanilla into the Thermomix bowl and blend 30 sec/speed 6. Check that the mixture is smooth and scrape down sides of bowl and repeat, 30 sec/speed 6.
Press mixture into the prepared tin and bake 15 minutes. Cool slightly.
Without washing the Thermomix bowl, place chocolate and 50g of the chopped peanuts into the bowl. Melt chocolate 8 min/50°C/reverse/speed 1 Stop and scrape down sides of bowl around the 4 minute mark.
Spread on top of base and sprinkle with the remaining nuts. Refrigerate for at least 4 hours before slicing and serving.