While the potatoes are cooking, heat 2 tbsp from the 250ml of oil in a frying pan over medium high heat, once the oil is hot add the diced onion and cook until golden and sweet tasting, add the cooked potatoes to the frying pan and crush with a potato masher, add salt to taste, usually about 1/4 tsp. Reserve. Wash up the frying pan and dry.
Add the remaining oil to the cleaned frying pan and place over a medium heat. To soften the corn tortillas so they fold around the filling, quickly dip each one into the warming oil, allowing as much oil as possible to drain back into the frying pan, then place on a baking tray, in a single layer.
Allow the oil to continue to heat up to frying temperature, about 180°C or until you dip a corn tortilla into the oil and it bubbles furiously.
Meanwhile, place 50g of the potato mixture down the centre of the softened tortillas, top with 10g of the Chihuahua cheese and fold in half.
Turn the oven on to 120°C and line an oven tray with paper towel, this is where you will put the crispy tacos to keep warm as you cook them.
When the oil is ready, lower a taco one at a time on its side, cook for about 30 seconds on each side or until the cheese has melted and the outside is golden and crispy.
When done, lift out of the oil and let drain, place on the paper towel and place in the oven while you cook the others.
When you are ready to serve, gently heat the jar of tomatillo sauce in a sauce pan, when just simmering, pull off the heat, reserve.
Place one crispy taco on a plate, top with 1/4 cup of tomatillo sauce, 1 tbsp of crème fraiche, a sprinkling of diced and rinsed white onion and a fine grating of pecorino cheese.