Heat 2 tablespoons of olive oil in a pan over medium heat.
Add onions and sauté for 4-5 minutes until onions are translucent.
Add mushrooms and cook for 10-15 minutes or until all liquid evaporates and mushrooms are slightly brown
Add in ½ teaspoon of salt and pepper.
Transfer mushroom to a bowl and set aside.
Transfer the mashed potatoes in a large bowl. Add salt, flour and mix everything well.
Place about 2 tablespoons of mashed potato mixture into a palm of your wet hand.
Flatten potatoes into a disk and place about 2 teaspoons of mushroom filling inside the disc.
Seal the edges together.
Continue shaping potato cakes until all potatoes and filling have been used.
Heat 3 tablespoons of olive oil in a large non-stick pan over medium heat.
Cook all potato cakes for 4-5 minutes on each side or until crispy and brown.
Serve immediately with sour cream.
