Heat 1 tablespoon of butter in a large skillet over medium heat.
Add the sweet yellow onion to the pan along with the leaves from one sprig of fresh thyme and cook, stirring often and adding bits of water when needed, for 30 minutes, or until caramelized.
Add the minced garlic and cook, stirring constantly, for 1 minute.
Season with sea salt and freshly cracked pepper, to taste. Remove from the heat.
In a large bowl, mix the mashed potatoes and caramelized onions until well combined.
Add the shredded Gruyere cheese, whisked egg, and 2 tablespoons of flour, fresh parsley, then season with sea salt and freshly cracked pepper, to taste; mix well.
Using your hands, divide the mixture into equal portions. Roll each portion into a compact ball then flatten into a pancake about a 1/2-inch-thick. I got 11 pancakes out of my mixture.
Roll each portion into a compact ball then flatten into a pancake about a 1/2-inch-thick.
Place the remaining 1/4 cup of flour in a shallow plate and season with a bit of sea salt and freshly cracked pepper, to taste.
Lightly dredge each side of the potato pancake in the flour.
Heat 2 teaspoons of vegetable oil plus 2 teaspoons of butter in a large non stick pan over medium heat.
Add the potato pancakes, in batches, until they’re golden brown and crispy on both sides, 3 to 4 minutes.
Add the remaining 2 teaspoons of vegetable oil and 2 teaspoons of butter to the pan for the second batch.
Transfer the pancakes to a paper towel-lined plate to cool a bit before serving.
Serve the potato pancakes topped with sour cream and chopped green onions.
Side Note: Don’t crowd the pan while cooking and do not flip the pancakes too soon or they won’t develop a yummy crispy crust!