Jerusalem artichoke soup with pesto

Ingredients

• 400 g Jerusalem artichoke
• 200 g celeriac
• 200 g potatoes, floury cooking
• 1 leek, white and light green only
• 2 tbsp butter
• 800 ml vegetable stock
• 100 g cream
• 1 handful of herbs (parsley, basil, rocket)
• 4 tbsp olive oil
• 20 g hazelnuts
• Salt
• Piment d'Espelette
• Vegetable oil, for frying
• 100 g cream cheese
• 2 tbsp lemon juice
• 1 tsp black cumin