Oil (for the baking sheet)
1 pound small red-skinned potatoes, halved
2 tablespoons olive oil, divided
1/4 teaspoon salt, divided
1 pound asparagus, bottoms trimmed and cut into 1 1/2-inch lengths

For the Dressing:
3 tablespoons lemon juice
1 teaspoon finely grated lemon zest
1 teaspoon Dijon mustard
1/8 teaspoon salt
1/3 cup extra virgin olive oil
Freshly ground black pepper
1 tablespoon chopped fresh tarragon