Put the oil and garlic in a pot and simmer on medium heat for 15 minutes. The garlic should be golden brown but not burnt. Transfer to a heat proof dish and refrigerate overnight.
Horseradish Garlic Mayo
Whisk together all ingredients and set aside. Season with salt and pepper to taste
Potatoes
toss the potatoes with salt, pepper, and a couple Tablespoons of roasted garlic oil. Roast in a 400 degree Fahrenheit oven for 20-25 minutes until golden brown and soft.
Take out of the oven and transfer to a bowl and use a potato masher to lightly "smash" the potatoes, but not into a smooth mash. transfer to plates and top with the horseradish mayo, thinly sliced red onion, and fresh dill.