For the latkes: Fill a pot three-quarters of the way up with water and add the potatoes. Bring the water to a boil, and then turn down the heat to a low boil. Boil until the potatoes are completely cooked (a knife slides in very easily), 20 to 30 minutes.
While the potatoes are boiling, heat up a pan over medium heat with 1 tablespoon butter and 1 tablespoon olive oil. Saute the leeks with the garlic until soft with no color. Season well with salt and pepper, lower the heat to medium-low and cook for another 3 minutes. Then take off the heat.
Once the potatoes are ready, place in a large bowl and mix in the sauteed leek mixture, nutmeg, the remaining 5 tablespoons butter and the remaining 1 tablespoon olive oil. Season well with salt and pepper, and reserve.
Whisk the eggs in a shallow bowl or dish and set aside. Add the breadcrumbs and the flour to two separate plates. Season the flour well with salt and pepper.
Roll a ball with the potato mixture that easily fits in the palms of your hands, about 2 tablespoons, and flatten slightly to make a patty. You don't want them too thick or too big. Dredge the potato patty with the flour, shaking off the excess. Dunk in the eggs and then coat with the breadcrumbs.
Get a large pan hot over medium-high heat, add an inch of canola oil and fry when the temperature reaches 350 degrees F. Remove from oil when the latkes are golden brown, 2 to 3 minutes. Serve hot with the garlic cumin sour cream.