Put cheddar, monterey jack, and cream cheese into the bowl of a food processor and process until well combined and smooth, 1-2 minutes. Divide cheese mixture into 12 equal portions, roll each between the palms of your hands into a ball, then flatten into a 1 1⁄2" disk. Transfer cheese disks to a plate, cover with plastic wrap, and chill in the refrigerator until firm, about 30 minutes.
Grate potatoes on the large holes of a box grater. Working with small handfuls at a time, squeeze out moisture from potatoes and transfer potatoes to a large bowl. Add eggs, scallions, jalapeno peppers, matzo meal, and stock, season to taste with salt and pepper, and stir until well combined.
Pour oil into a large deep skillet to a depth of 1 1⁄2 and heat over medium heat until hot but not smoking. Working in batches, shape 1⁄4 cup of the potato mixture into a 3" loose disk, put 1 cheese disk in center, and fold potato mixture up and around disk completely enclosing cheese disk with the potato mixture. Fry in hot oil, turning once, until golden brown and crisp on the outside, 5-7 minutes per batch. Transfer latke poppers with a slotted spatula to paper towels to drain. Season to taste with salt, if you like.