To make the sauce, add all sauce ingredients (lemon, olive oil, garlic, dijon) along with some salt and pepper to a blender and blend until the sauce is totally combined. Season to taste with salt and pepper
On a parchment paper lined baking sheet, add your quartered fingerling potatoes and pour about half of your lemon garlic sauce onto them. Season with more salt and pepper and toss to combine until the potatoes are all evenly coated.
Spread the potatoes out in an even layer across the baking sheet and roast for 20 minutes. Remove from the oven and toss with a spatula. Roast for another 15 minutes
Remove the potatoes from the oven and toss them in some of the remaining vinaigrette. Start with one tablespoon at a time and stop when you feel that the potatoes are lemony enough. I added 3 tablespoons, and the potatoes were very lemony + saucy that way (which is just how I like it 😉)
Turn your oven to broil and broil the potatoes for a few more minutes, watching carefully, giving the raw garlic a chance to cook just a little and the potatoes a chance to brown a bit more
Top with fresh dill and red pepper flakes (optional)