- 3 pounds medium sweet potatoes, peeled and each cut lengthwise into 8 spears
- 1/4 cup vegetable oil
- 1 1/4 teaspoons salt
- 5 tablespoons unsalted butter
- 1/3 cup molasses (not robust or blackstrap)
- 1/3 cup bottled horseradish (including juice)
- Put oven rack in lower third of oven and preheat oven to 450 degrees F.
- If potato spears are very long, halve them diagonally. Toss potatoes with oil and 3/4 teaspoon salt in a large bowl, then spread in 1 layer in a large shallow baking pan (1 inch deep). Roast in lower third of oven, turning once or twice, until tender, 18 to 22 minutes. Leave oven on.
- While potatoes roast, bring butter, molasses, horseradish (with juice), and remaining 1/2 teaspoon salt to a boil in a small heavy saucepan, stirring, then reduce heat and simmer, stirring occasionally, until slightly thickened and reduced to about 3/4 cup, about 5 minutes.
- Transfer mixture to a blender and pure 30 seconds (use caution when blending hot liquids). Pour glaze through a fine-mesh sieve into a heatproof bowl, pressing on and discarding solids. Drizzle glaze over cooked sweet potatoes and gently toss until coated. Just before serving, bake glazed sweet potatoes in lower third of oven until hot, 3 to 5 minutes.