Whisk warm water and yeast in a bowl until dissolved.
Stir in 500g of flour to form a loose batter.
Cover and let rise in a warm place until doubled and bubbly.
Combine remaining flour, salt, sugar, olive oil, and batter in a mixer.
Knead for 7 minutes until smooth or until dough leaves the bowl sides.
Roll dough into a 2cm thick sausage and form a large pretzel shape.
Place on a greased tray and let rise for 30 minutes.
Preheat oven to 220°C.
Brush pretzel with egg wash and sprinkle with optional seeds or salt.
Bake for 30 minutes until golden-brown.
Melt butter in a pan and fry chopped onion until softened.
Add potatoes and corned beef, frying until crisp and golden-brown.
Stir in Worcestershire sauce and parsley, then season with salt and pepper.
Boil a large pan of water and dip whole eggs for 20 seconds.
Add vinegar to water and poach cracked eggs individually for 3 minutes.
Serve corned beef hash topped with eggs and pieces of the pretzel.