Use a mandolin to slice the vegetables very thin rounds – about 1/8 inch or thinner. Place the sliced beets in one bowl and the sliced sweet potatoes in another. Toss each with 1 tablespoon oil and a good pinch of salt. Cover and let sit for 30 minutes, to allow some of the liquid to sweat out of the vegetables.

Drain off the liquid (about 1/4 from the beets and few tablespoons from the potatoes) and pat dry with a paper towel. Arrange in a single layer on parchment lined baking sheets.

Bake at 300ºF for 1 hour and 15 minutes, turning halfway through. Remove from the oven and let cool (the chips will continue to crisp). Adjust the seasoning to taste.

Meanwhile, make the dip by mixing the cream cheese and milk until smooth. Stir in the horseradish, vinegar, herbs, and salt and pepper. Cover and refrigerate 30 minutes to let the flavors meld. (The horseradish will taste stronger after the dip is chilled.)