In a large skillet, fry the white onion in the butter until soft and translucent. Add in the fresh garlic and saute until it's browned and fragrant. Set the skillet aside off of the heat.
In a large bowl, mix the mashed potatoes, flour and eggs together until they are completely, combined together and smooth.
Mix in the cheeses, fresh dill and the salt.
Add in the onions and garlic from the skillet and combine everything completely.
In the same skillet, melt another 1-2 tbsp pf butter again over medium-low heat.
Scoop out a large golf ball sized amount of dough - a large cookie scoop works perfectly for this - and place into the frying pan.
Flatten the potato ball until it's around 1/3 of an inch thick. If the cakes are too thick they will not heat enough in the middle for the egg to be safely cooked to 165°F.
Fry on the medium low heat for around 4-5 minutes per side, until the cakes are browned and crispy on the outside and are heated in the middle to at least 165 °.F to ensure raw egg safety.
Remove and plate, serving with a dollop of sour cream, salt and pepper!
Notes
If you make your potato cakes too thick, they will not cook to a safe temperature in the middle. Remember that they have raw egg in them and thus much reach an internal temperature of 165 °F. If they are thicker than 1/2 inch, they won't cook in the middle. I feed my food to my kids and elderly relatives so I am SUPER safe when it comes to raw eggs.