Preheat oven to 450℉, and then bring water to boil in a large pot. Add salt, baking soda, and potatoes and stir. Return to a boil, and then reduce to a simmer. Simmer for about 7-10 minutes, until potatoes are cooked halfway. It will be easy to pierce a potato piece, but they aren't entirely soft yet.
While potatoes are simmering, combine oil, garlic, rosemary, salt, and pepper in a large bowl that can accommodate all the potatoes.
When potatoes are finished simmering, drain them and then allow the pot to sit uncovered for 1-2 minutes to allow them to steam off. Then toss all the potatoes in the oil and spice mixture until well-coated. Toss roughly, to ensure the outer layer of potato gets sufficiently mashed on all the pieces.
Transfer the potatoes a lightly greased baking sheet, and spread them out into a single layer. Bake for 20 minutes, then flip gently and spread them out again. Bake for an additional 15-20 minutes, or until golden brown and done to your liking. You may have to flip/spread them again another time or two to ensure no pieces are burning.
Remove from the oven and sprinkle with a touch more salt or extra spices if you like. Then serve.