Cucumber and Lettuce Vichyssoise from 'River Cottage Veg'

Ingredients (14)

• 2 tablespoons (60g) butter
• 2 leeks, trimmed (white and pale green parts only) and sliced, or 1 large onion, sliced
• 1 large, starchy potato (about 
8 ounces/250g), peeled and cut into large chunks
• 1 quart vegetable stock
• 2 cucumbers, peeled and cubed
• 2 Little Gem or butterhead lettuces, shredded
• 3 tablespoons heavy cream or crème fraîche
• Sea salt and freshly ground black pepper
•  
• 1/4 cup (60ml) canola or olive oil
• 4 slices of bread, crusts removed, cut into cubes
•  
• Chopped chives
• Heavy cream or crème fraîche