Drain potatoes. In a large saucepan over high heat, combine vinegar and 2 quarts water. Bring to a boil.
Add potatoes and cook for 5 minutes. Drain well and spread in a single layer on rimmed baking sheets lined with paper towels. Dry five minutes.
In a Dutch oven, large pot, or deep fryer, heat oil to 400 degrees. Add 1/2 of potato slices and cook, stirring and flipping constantly with wire mesh spider or slotted spoon, until potatoes release no more bubbles, about 3 to 5 minutes (smaller chips may cook faster than large ones and should be removed from the oil as they finish).
Transfer potato slices to a rimmed baking sheet lined with paper towels, and sprinkle with salt. Repeat with remaining potato slices.
To make the nachos:
Preheat oven to 450 degrees. Transfer potato slices to a broiler-proof pie plate or serving platter.
Top with cheese and bacon. Bake until the cheese is hot and bubbly, about 3 minutes. Remove from oven and top with sour cream, tomato, scallions, and jalapeño slices, if using.
Potatoes: Opt for starchy potatoes like Russets so they're sturdy enough to slice, cook, and hold toppings. For even cooking, cut into slices of equal thickness (I suggest using a mandolin).
White vinegar: Parboil the potato slices in water and 2 tablespoons of vinegar. The acid will help the potato slices hold their shape while cooking.
Bacon: Crisp it up in a skillet or on the stove; here's how to fry bacon perfectly.
Scallions: You could also substitute chives, dill, or your other favorite herbs.
Jalapeño: If you want to use this but are seeking a slightly less spicy option, remove the ribs and seeds before slicing; that's where most of the heat resides.
Yield: Each recipe as listed makes 4 servings of Irish Nachos that include 4 ounces of potato slices each.
Make ahead: This is best enjoyed hot from the oven, but feel free to slice and store the potatoes in a bowl of water up to 24 hours before to get a jumpstart on prep.
Storage: If you have any leftover Irish Nachos, store in the refrigerator up to 3 days. Reheat in the oven at 450 degrees until the potatoes are warm and the cheese gets melty again, about 10 to 15 minutes.
Baked Irish Nachos: To bake instead of fry the potato slices, follow step 1 and 2 as listed. Instead of step 3, preheat your oven to 425 degrees. Toss the potato slices in oil, salt and pepper, and arrange on a baking sheet in a single layer. Bake in the preheated oven, stirring occasionally, until potatoes are crisp and golden brown, 25 to 30 minutes. Then turn the oven up to 450 degrees and proceed with the recipe as written.
Waffle fries: If desired, skip the first 3 steps and start with frozen waffle fries, cooked according to package instructions.
Cheese swap: Feel free to replace the shredded cheddar with any crumbled cheese, shredded cheese, or cheese sauce that you like.
Toppings bar: Consider serving with bowls of sliced avocado, chopped cilantro, finely diced white onion, chopped olives, and/or diced bell peppers so each diner can garnish their serving with personal favorites.