Falafel with tahini

For the falafels:

1/2 onion

1 clove of garlic (peeled)

250g soaked chickpeas (or 125g dried)

1 green chilli

3 springs of parsley, picked

1 small bunch of coriander, leaves and top part of stems only

1/2 tsp ground cumin

1 tsp freshly ground cardamom pods

1/2 tsp salt

2 tbsp garam flour

1 tsp baking powder

For the tahini:

125g tahini paste

1 garlic clove, peeled and minced

a pinch of salt, plus more to taste

juice of 1 lemon, plus more to taste

120ml water