Preheat the oven to 350° F.

Peel the potatoes and cut them into large chunks. Place in a bowl with cool water to cover while you assemble remaining ingredients.

In a large bowl, whisk the eggs together with the onions, matzoh meal, salt, pepper, Essence and thyme. Set aside.

Place about half of the potatoes in the bowl of a food processor and pulse until very finely chopped. Working quickly, transfer the chopped potatoes to a fine mesh strainer set over another bowl. Using a rubber spatula, press firmly onto the potatoes repeatedly to release as much of the starchy water from the potatoes as possible. Immediately add the potatoes to the egg mixture and repeat with the remaining potato chunks. Discard the potato water/starch remaining in the bowl.

Place two tablespoons of the rendered chicken fat into a 9-inch square baking pan and place in the oven to heat for approximately 5 minutes.

Remove the pan from the oven and tilt pan to evenly distribute the melted fat, coating all sides of the pan evenly. Pour the potato mixture into the warm pan and drizzle the remaining fat over the top of the kugel. Bake uncovered until the kugel is golden brown and crispy on top, about 1 hour and 10 minutes. Remove from the oven and allow to cool at least briefly before cutting and serving. It will cut easier if made in advance and then can be reheated in a hot oven.

Garnish with sour cream and chives if desired.