Place a rack in middle of oven; preheat to 425°. Poke potatoes all over with a fork; rub with oil. Bake directly on oven rack until very soft when squeezed and skins are crisp, 50–60 minutes. Let cool just until you can hold them.
Using a serrated knife, slice potatoes in half lengthwise and scoop flesh into a medium bowl. Add sour cream, butter, chives, and tarragon (if desired); season generously with salt and pepper.and place a slice of cheddar on each of them.
Divide among 4 potato skin halves, piling gloriously high—don’t pack too tightly. (And what about the leftover skins? We say add butter and salt and snack on them.)
Increase oven temperature to 450°. Bake potatoes on a rimmed baking sheet until filling is puffed and browned in spots, 20–25 minutes.
