Heat a big pot of water until it boils then add baking soda and potatoes. When it boils again let it boil for 2-3 min then turn it off and discard the water. Return potatoes to the same pot over warm but turned off stove and mix with a wooden spoon for 1 min so that potatoes become a little mushy.
Drizzle olive oil (I would recommed 1 tbsp if potatoes are the main dish and 2 tsp if they are part of many dishes) over potatoes and add salt and pepper to taste. Mix together well.
Arrange potatoes evenly in one layer over baking tray with baking paper and scatter rosemary on top. Roast at 260 °C for 20-25 min.
*The tip on how to get those crispy potatoes came from Just a Little Bit of Bacon.*You can also use purple/blue potatoes. They're delicious as well when roasted.