Preheat the oven to 190°C.
Grease a baking tray with a little butter.
Mix flours, butter, bicarbonate of soda, salt, peppercorns, and buttermilk to form a soft dough.
Shape the dough into a loaf, dust with flour, and bake for 45-50 minutes.
Heat oil in a pan and fry onions and garlic for 4-5 minutes until softened.
Add the diced potato and fry for a further 5-6 minutes.
Add chicken stock, bring to the boil, then simmer for 4-5 minutes.
Add sliced celery and simmer for 5-8 minutes until tender.
Stir in parsley leaves and double cream, then heat through.
Blend the soup until smooth, strain, and season.
Bring salted water and vinegar to a simmer.
Poach eggs in a vortex for 3-5 minutes until the whites set.
Chop celery leaves and drizzle eggs with oil and celery salt.
Serve soup in bowls with a poached egg on top and buttered soda bread.