Preheat the oven to 350°F.

To make the queso, in a 2-quart saucepan, heat the butter on medium-low. Add the onion and jalapeños and while occasionally stirring cook until softened, about 5 minutes. Add the garlic and tomatoes and cook for 30 more seconds.

Whisk together the cornstarch, milk, and water until well combined then pour into the pot. Bring to a simmer and while stirring, cook for a couple of minutes until it thickens, then add the American cheese. Turn the heat down to low and while stirring cook until the cheese has melted. Stir in the salt, cumin, cayenne then taste and adjust seasonings. Turn off the heat.

For the soft cheese tacos, pour the oil into a 9x13 baking dish. To quickly warm the tortillas, place them in the baking dish (it’s okay if they overlap) and make sure they get covered in the oil. Place uncovered in the oven for 3 to 5 minutes or until soft and warm. Remove the tortillas from the baking pan and keep covered.

To assemble the tacos, place a warm tortilla on a clean surface and add 1/4 cup of the shredded Colby Jack down the center of the tortilla then layer on top 1 teaspoon of the onions, if using. Roll the tortilla then place seamed side down in the baking dish.  Repeat with the remaining tortillas.

Bake covered for 10 to 15 minutes or until the cheese in the tacos has melted. As they near the end of baking, reheat the queso on low, stirring occasionally. Once the cheese in the tacos has melted, remove from the oven and then pour the queso evenly over the tacos. Serve warm with sliced pickled jalapeños for garnishing on the side.