Making duchess potatoes is like turning lemons into lemonade. You’re taking a common potato and turning it into something very different and very good-looking.
The mashed potatoes must be stiff in order to hold their shape. Be sure to thoroughly seed the tomatoes, so they don't add too much moisture.
Preheat oven to 450°. Line a baking sheet with parchment paper.
Boil potatoes in a large pot of salted water until fork-tender, 15–20 minutes. Drain potatoes well, then mash until smooth.
Stir in cream, butter, and egg yolks just to incorporate; fold in tomatoes and salt. Transfer potatoes to a pastry bag fitted with a 1½-inch star tip.
Pipe six mounds of potatoes onto the prepared baking sheet. Bake potatoes until tops are lightly browned, 15 minutes; serve immediately.
% Daily Value*
Total Fat 16g 24%
Saturated Fat 10g 50%
Cholesterol 109mg 36%
Sodium 19mg 0%
Carbs 29g 9%
Fiber 2g 8%
*Percent Daily Values are based on a 2,000 calorie diet.