Peel potatoes and cut them into 2 to 3-inch chunks. If potatoes are on the smaller size, you can quarter them. If they are medium, cut them in sixths. Larger potatoes should be cut into 8 pieces.
Bring 2 quarts of water to a boil in a pot. Add salt and baking soda and potatoes and stir.Reduce heat to maintain a simmer. Simmer for 10 minutes.
Preheat oven to 450 degrees.
While the potatoes are cooking, heat the oil in a small pot or skillet. Add garlic and rosemary and cook just until the garlic is starting to turn golden. Remove from heat and pour oil through a fine-meshed sieve into a bowl.
Drain potatoes well and return them to the hot pot for a minute to evaporate the water on them.
Toss potatoes and oil in a large bowl. Season with a little salt and pepper. Stir the potatoes roughly. This is the key to getting them really crispy. You don't want the outside edges to be smooth. You want them to almost look like they are coated in paste.
Spread potatoes out on a baking sheet. Bake for 20 minutes. Give them a good stir and bake for another 30 to 40 minutes.
Check for seasoning and add more salt and pepper if desired.