Preheat the oven to 400F/200C. Cut slits into each potato to look like an accordion, each cut should be deep enough for the potato to open up but not all the way through, so it stays together. Take your time doing that as it is the most challenging task of the recipe by far. (See tips in the post.)
Rinse each potato in cold water afterwards to get rid of the extra starch between slices, otherwise they stick together. Dry with paper towel.
In a large bowl combine the olive oil, smoked paprika, grated garlic or garlic powder and salt. Dunk each potato into the mix and place on a shallow roasting pan. You will have the oil mixture leftover after all potatoes are coated, reserve it for later.
Roast in the preheated oven for 30 minutes, then take out of the oven and brush the oil mixture on the potatoes making sure it’s getting inside the slits. This part is very important for the success of the recipe. Roast for 20-30 minutes longer until crispy on the outside and cooked all the way through. Larger potatoes might take longer.
Mix the chopped parsley, lemon zest and juice with grated garlic, the olive oil and salt and serve with the hasselbacks on the side.