Parsnip soup with chunky croutons

Ingredients

• 1 tbsp olive oil
• 2 garlic cloves, finely chopped
• 600g parsnips, cut into 1cm/½-inch cubes
• ½ tsp dried red chilli flakes, plus extra to serve
• 1 litre hot vegetable stock
• 200ml double cream
• salt and freshly ground black pepper
• 3 thick slices good bread, such as sourdough, cut into 2.5cm pieces
• 55g Gruyère cheese, finely grated (optional)