Remove the green, wash under running water, let it drip off or spin it dry with a salad spinner. Then chop coarsely.
Peel and press the garlic cloves.
Put all ingredients up to and including hazelnuts into a blender or food processor. Add 50ml olive oil and crush into a pesto. Depending on the mixer/food processor, you will need more olive oil so that the pesto can be processed evenly.
If you use up the pesto immediately you can add the yeast flakes immediately, otherwise I would wait until serving with it.
Fill the pesto into a sealable glass and cover with olive oil. Store in the fridge and use within 3-4 days.