Cook potatoes in plenty of salted water until cooked through.
Add 2 tablespooons butter to medium skillet and heat to medium. Add onion and cook about 3 minutes, until softened. Add crushed garlic during last 30 seconds of cooking onions. Off heat and set aside. Note: If adding panchetta, cook it a little with the onions and garlic just until the fat becomes translucent.
In a large bowl, combine potatoes and roughly mash with potato masher. Add eggs, onion/garlic mixture, meat, sour cream, cheese, chives and green onions. Add 2 teaspoons salt, black pepper as desired. Adjust the texture with a bit of milk if necessary.
Preheat your oven to 400°F (190°C) and line a baking sheet with parchment paper.
On the baking sheet, using a ring mold*, scoop potato mixture to shape the cakes, I made mine over 2 inches thick, but you can make yours less thick to make more. Press down slightly with fingers or a spatula. Sprinkle with additional cheese (Parmesan is great here), crushed red pepper flakes, if desired. Remove the ring mold and repeat the process.
Bake in the oven at 400°F (190°C) for 15-20 minutes, or until golden and serve warm with pat of butter on each and sprinkle with additional chives.
The potato cakes freeze wonderfully for up to a month and travel great in lunches.
*If you don't have a ring mold, I cut a length of an aluminum foil pan at least as tall as I wanted my cakes. Then I wrapped them around a glass to create a good circle and taped the piece all around to retain the shape. This worked great!
p.s. If you want, shape the cakes by hand. Not as pretty, but tastes just as delicious.