Ingredients:

• 2 pounds Idaho® russet potatoes, peeled and quartered (4 medium)
• 2 tablespoons cooking oil, such as canola
• 2 tablespoons unsalted butter
• 3 medium yellow onions, peeled and diced (1 ½ pounds)
• 2 large eggs
• ⅓ cup matzo meal
• 5 ounces spinach leaves or baby spinach, slivered or roughly chopped
• Kosher salt
• freshly ground black pepper
• 8 ounces sour cream, to garnish

Directions:

1. Preheat oven to 375ºF and set oven racks in the top and bottom of the oven.
2. Spray or lightly oil two baking sheet pans. Set up a food processor with the chopping blade.
3. Place potatoes and 2 teaspoons salt in a large pot and cover with cold water by an inch. Bring to a boil and cook for 20 minutes or until potatoes are tender. Drain, mash well, and set aside to cool.
4. Melt butter with oil over medium heat in a large skillet. Cook onions, stirring occasionally, for 20 minutes, to brown. Scrape onions into the bowl of the food processor. (Don't clean the skillet - you'll use it for the spinach.) Add eggs, 1 teaspoon of salt and 1/4 teaspoon of pepper to onions and pulse several times, until the onions are finely chopped. Scrape the onion-egg mixture into the bowl with the potatoes. Add matzo meal. Mix thoroughly and set aside.
5. Add the chopped spinach to the skillet and sauté over medium heat, stirring constantly, until wilted (a minute or two), add wilted spinach to the potato mixture and stir through.
6. Scoop up a heaping tablespoon of potato mixture, roll it into a ping pong-sized ball and place it on one of the prepared pans. Repeat until you've used up all the potato mixture, spacing the balls about 1/2 inch apart. You should get about 50 pieces.
7. Push your thumb down on the center of each ball to flatten it slightly and make a depression similar to how you'd make thumbprint cookies.
8. Bake knishes for 30 minutes in the top and bottom of the oven, switching the position of the trays half way through. Turn the oven up to broil and cook 2-3 minutes, checking every minute, until the knishes on the top shelf get some nice brown spots. Switch the position of the trays and let the second tray of knishes brown for a minute or two.      
9. Remove trays from oven and let knishes cool for 10-15 minutes. Set knishes out on a platter or serving tray. Dollop a little sour cream in the center of each knish and serve.