Preheat oven at 425°F (220°C). Place the rack on the bottom shelf of the oven. The potatoes will get more golden and crispy here, faster.
Take a large baking sheet (it is important that there's enough room to spread the potatoes around and not cram them, otherwise they will steam and not become crunchy). Add the olive oil and place the tray on the bottom rack in the oven while you prepare the potatoes.
Peel and wash the potatoes. Cut into equal pieces, around 1 inch (3 cm) chunks.
Fill a pot with 2 liters of cold water, add 1 1/2 tablespoons of salt, and add the potatoes. When the water starts to boil, turn the heat down to a simmer. Cook for 10 minutes. The potatoes should be soft with just a bit of a hard center, when poked with a knife.
Meanwhile peel and smash the garlic. Holding the rosemary sprigs at the top, pull down to remove all the rosemary leaves. Then chop and add to a small bowl. Drizzle with oil and make sure each rosemary piece is well coated, so it won't burn in the oven. Set aside. (or you can use dry rosemary)
When the potatoes are done, drain in a colander. Shake the colander to fluff the potatoes. You want to rough them up and mash the outside layer. This will ensure that perfect crispiness we are looking for. Let sit for another 4-5 minutes until the steam has evaporated, so there won't be too much moisture left. This is key for the end result.
Using an oven mitt, take the tray out of the oven. Add the potatoes in the hot oil in the tray (be careful not to splash yourself). Add the salt, pepper, and paprika. I like to add the whole, smashed garlic cloves and the rosemary at this point, because I like a stronger aromatic flavor (even if some bits will get a bit burnt, they will remain in the tray and the potatoes won't get affected). But if you are worried about it, you can add your garlic and rosemary after the first 20-25 minutes of roasting, when you turn the potatoes. Coat all the potatoes and garlic cloves well with the oil, then spread everything out in a single layer, and individual pieces, as much as possible.
Place the baking sheet back on the bottom rack of the oven. Roast for 20-25 minutes without touching them. After the first 20-25 minutes, add the garlic and rosemary if you didn't add them from the beginning, turn the potatoes and try to spread them around so they are individually scattered. Cook for another 10-20 minutes. Check after the first 10 minutes. If you are happy with the result, take the potatoes out. If you want them more golden and crispy, roast them a bit longer. There isn't an exact roasting time for all potatoes, as this depends on the starch and sugar content of each potato type. Older potatoes take longer to cook as they have less sugar and more starch. So you will have to adjust as you go. But the end result should be nice golden brown and crispy potatoes all over.
Once the potatoes are perfectly roasted, transfer to a serving plate. Season with more salt and pepper to taste (if needed), sprinkle some Parmesan cheese or fresh parsley, and enjoy while still hot.