Using a sharp knife, cut slits into the potatoes that are approximately 1/8 of an inch apart and do not cut all the way through (you can use chopsticks or something similar to brace each side of the potato and stop your knife from going through).
Place cut potatoes in a bowl. Mix with the olive oil (2 tablespoons) and plenty of salt and pepper.
Place cut side up onto a parchment covered rimmed baking sheet.
Roast for approximately 60 minutes, or until potatoes are tender and golden brown on the outside.
Meanwhile, add dill (2 tablespoons), scallions (4), kosher salt and pepper to taste, lemon zest, and lemon juice to a food processor and pulse until finely chopped. Add the sour cream and mayonnaise and pulse until combined. (alternatively, you can just chop the dill and onions finely and mix everything in a bowl)
Serve the potatoes warm with the dip.
To make these in advance, follow all instructions as directed. Refrigerate the dip and the potatoes overnight, and reheat the potatoes on a roasting pan at 400 degrees for 15-20 minutes, until warmed and crispy.
If you want a crispier, more decadent potato: halfway through baking, you can brush them with more olive oil or even some melted butter, so it seeps into the crevices a bit more.
The provided nutrition information does not include any added sodium from seasoning to taste, any optional ingredients, and it does not take brands into account. Feel free to calculate it yourself using this calculator or by adding the recipe to Yummly.