Preheat the oven to 160°C and line 2 large baking sheets with parchment paper.
Trim and peel the beets, then slice them into very thin rounds about 2 millimeters thick using a mandoline or a sharp knife.
Place the beet slices in a large bowl and toss them with the olive oil, 1/4 teaspoon of the sea salt, and the black pepper until lightly coated.
Arrange the beet slices in a single layer on the prepared baking sheets, keeping them from overlapping so they can dry and crisp evenly.
Bake for 20 minutes, then rotate the pans and flip the slices with tongs or a thin spatula.
Continue baking for 20 to 30 minutes more, removing smaller slices as they crisp and keeping larger slices in the oven until the edges are dry and lightly curled.
Transfer the baked beet chips to a wire rack and let them cool for 10 minutes so they become crisper.
While the chips bake, stir together the Greek yogurt, dill, chives, lemon juice, grated garlic, and remaining 1/4 teaspoon sea salt in a small bowl until smooth.
Taste the herbed yogurt and adjust with a little more lemon juice or salt if needed.
Serve the cooled beet chips on a platter with the chilled herbed yogurt alongside for dipping.