Artichoke soup and parsnip crisps

Name: Artichoke soup and parsnip crisps
Prep time: 10 min
Cook time: 30 min
Total time: 40 min
Cuisine: British
Ingredients: 1 tbsp mild olive oil; Knob of butter; 2 onions, finely diced; 2 garlic cloves, crushed; 1 medium (about 150g) floury potato; 6 medium Jerusalem artichokes; 1 litre vegetable stock; 250ml milk, hot; 2 tsp thick double cream, to garnish; Extra-virgin olive oil, to drizzle