1.) Preheat the oven to 400 degrees F.
2.) Thinly slice the potatoes with a knife or a mandolin; a food processor with a thin setting for slicing can work well too. Place the potato slices into a bowl of cold water to rinse some of the starch off.
3.) Remove the potato slices from the water and drain well before laying them on some paper towel to dry. Pulling out excess moisture prior to baking will help the chips get nice and crispy.
4.) Lightly spray a baking sheet lined with parchment paper with cooking oil spray. Place the potato slices in an even layer on the baking sheet. Lightly brush the potatoes with the vegetable oil and sprinkle them with half of the salt and pepper. Place the potatoes in the oven for 8-10 minutes, then rotate the pan and bake for an additional 8 minutes, or until they are crispy and golden brown.
5.) While the chips are baking, prepare the dip. In a pan over medium heat, sauté the thinly sliced onions in 1 tsp of neutral oil and salt and pepper to taste. Allow the onions to cook down, stirring them occasionally until they start to brown slowly. Continue to stir as the onions cook down. If the onions begin to stick, scorch, or burn, add water to the pan 1 tbsp at a time to gently deglaze.
6.) Once the onions take on a beautiful brown color, remove them from the heat. Allow the onions to cool slightly before giving them a rough chop.
7.) Combine the chopped onions, sour cream, Greek yogurt, scallions, and the remaining salt and pepper in a bowl. Mix well and adjust the seasonings to taste.
8.) Pour the dip into a serving bowl and enjoy alongside the baked chips.