Step 1

To make the sauce, mix all of the ingredients together in a small saucepan: ketchup (1 cup), water (1/4 cup), vinegar (1 tablespoon), sweet paprika (1 1/2 teaspoons), cumin (1 teaspoon), salt (1 teaspoon), oregano (1/2 teaspoon) and sriracha (1/2 teaspoon). Cook at a gentle simmer, partially covered, for 5 minutes. Sauce can be made a day ahead and refrigerated until ready to use.

Step 2

Peel the potatoes and shred them on a box grater or in your food processor with the coarse shredding blade. Swish them in a bowl of cold water, pour out cloudy water, and repeat until the water is clear. Just before frying, drain them in a colander and dry them well by squeezing them between several clean absorbent dish towels. The dryer the better for getting them crisp and brown. Pour oil into a heavy, non-stick skillet over medium-high heat and fry the potatoes, in small batches, until they're golden brown. Transfer to a paper towel-lined plate and sprinkle with salt.

Step 3

Make the meat mixture in a large bowl or in a food processor. Combine ground meats with 1 cup of the onions and the garlic (2 tablespoons). Mix by hand or pulse a few times in the food processor, to combine. Add ketchup ( 3 tablespoons), cumin (1 teaspoon), paprika (2 teaspoons), smoked paprika (2 teaspoons) and 1 1/2 teaspoons of salt. Mix by hand or pulse just until combine. Form the meat into 8 thin patties.

Step 4

Cook patties in batches, on a preheated flat griddle or in a frying pan coated with a little vegetable oil, over medium heat, for 2-4 minutes per side or until they're cooked to your liking. (I suggest medium rare to medium). Season with salt and pepper, to taste.

Step 5

To assemble the fritas, spread some special sauce over the bottom half of a bun. Place a patty on top, add more sauce, some finely chopped raw onion and a big pile of shoestring fried potatoes. Spread a little sauce on the inside of the top bun and place it on top. Repeat with remaining burgers. Serve immediately.