Put the split peas in a bowl, add boiling water to cover and leave to soak for 30 minutes. Drain.
Dry-fry the bacon in a heavy-based saucepan for 2-3 minutes, until lightly coloured. Add the onion, carrot and celery and cook, stirring, for 2-3 minutes, without browning.
Add the stock and peas, bring to the boil, then cover and simmer for 30-40 minutes until tender. Purée in a blender until smooth. Return to the pan and add salt and pepper to taste.
Cut the bread into 1cm (½ in) dice and toss with the garlic to coat evenly. Spread on a baking sheet and toast under a hot grill, turning until golden brown. Serve the soup hot, sprinkled with the sippets and parsley.