Step 1Into a bowl, grate the potato, onion and apple and cover as you go with very cold water to prevent browning. Onto a kitchen towel or several layers of cheesecloth, directly grate the beet and sweet potato.
Step 2Pull the potato mixture out of the water, squeeze out as much liquid as you can with your hands, add to the beets and sweet potatoes and fold the towel over the mixture.Twist the ends towards the center and squeeze the liquid out of the shredded vegetables. Once you think you’ve extracted all the liquid, add some elbow grease and squeeze again; you’ll be shocked how much more comes out. Transfer the shreds to a large bowl.
Step 3Toss the shredded vegetables with the cornstarch until coated, then stir in the garlic, eggs, egg yolk, salt, thyme and baking powder until incorporated. The mixture should feel moist but not as soupy as a lot of latke batters.
Step 4Arrange two 10-inch, heavy-bottomed skillets on the stovetop (if you have only one skillet, you can make the pancakes one at a time. After you make and drain the first pancake, keep it heated in a 400-degree oven while you make the second pancake). Divide the peanut oil between the skillets and heat it over medium heat (resist the urge to crank up the heat under that oil; keep it at medium) until hot, 3 to 4 minutes. Divide the pancake mixture between the skillets, gently spreading it into an even layer but leaving a little room around the edges. And you don’t want to pack the potatoes down too much since this will prevent the pancakes from cooking through to the center.
Step 5Fry until the underside of each pancake is deep brown and crisp and the edges are lacy, 5 to 6 minutes. Using 2 spatulas, grab hold of each pancake and gently flip it, then fry until the undersides are browned and crisp, another 5 to 6 minutes. Drain on paper towel-lined plates.