Beef liver gravy, Estonian style

500 grams beef liver, cut into thin long strips (1 cm x 4-5 cm)
2 Tbsp plain/all-purpose flour
1 tsp black pepper
2-3 Tbsp oil
1 onion, finely chopped
200 ml cold water
100 ml sour cream
salt
fresh dill

To serve:
boiled potatoes
fresh dill, finely chopped
salted cucumbers, sliced

Mix flour with pepper.
Cut liver into thin strips**, drench in flour/pepper mix.
Heat oil in a frying pan, add liver and onion and brown on low heat.
Add any leftover flour, add cold water and heat, stirring regularly, until the sauce thickens. Simmer for 5-7 minutes.
Add sour cream, stirring regularly, and simmer on a low heat for another 5 minutes.
Season with salt, garnish with dill.
Serve with boiled potatoes and sliced salted cucumbers.