1 to 1 1/4lbs.golden beetsabout 5 medium beets that are close in size to the potatoes, plus 1 small beet for shaving
4Tbsp.extra-virgin olive oildivided
1 1/4tsp.kosher salt
1/2tsp.crushed fennel seed
1/2tsp.freshly ground black pepper
1small shallotthinly sliced
2Tbsp.chopped fresh dillplus more for garnish
Preheat oven to 425°F. Place potatoes and beets (all except smallest one) in a 13x9-inch baking dish. Toss with 1 Tbsp. of the oil and 1/2 tsp. of the salt. Fill pan with 1/4-1/2 inch of water. Cover with foil and bake for 50 to 60 minutes, until fork tender. Set aside and let cool until able to handle, about 30 minutes.
In the meantime, prepare dressing by combining remaining 3 Tbsp. oil, 3/4 tsp. salt, vinegar, mustard, fennel seed, and black pepper in a small bowl; whisk until smooth. Shave remaining small beet on a mandoline into thin slices. Set aside.
Peel cooled beets and discard skins. Slice beets and potatoes into quarters, or smaller depending on size. Transfer to a large bowl or serving platter. Add shaved beet, shallots, and dressing; toss to combine. Gently fold in dill. Garnish with additional herbs, if desired. Serve at room temperature.