Take a large pot and fill it up with water. Sprinkle in some salt to add some flavor. Let the water come to a boil.
Toss the potatoes into the pot of boiling water and let them bubble away for about 25 minutes, or until they're fork-tender.
Meanwhile, preheat the oven to 400 degrees Fahrenheit and prepare a parchment paper-lined baking sheet.
Once the potatoes are cooked, drain them and let them cool off for a few minutes. Then, toss them into a medium-sized bowl.
Add heavy cream, salt, pepper, and half of your butter to the bowl. Save the rest of the butter for later. Mash those potatoes until they're smooth and creamy (with a potato masher or blender or hand mixer on low speed).
Stir in the egg yolks. Beat on low and be careful not to overmix.
Prepare a pastry piping bag and a large star tip. Place potatoes into the piping bag and swirl them onto the prepared baking tray like a fancy ice cream cone.
For final touches, melt the remaining butter in the microwave for 20-30 seconds and brush it onto those beautiful potato swirls.
Pop the tray into the oven and let potatoes bake for 25-30 minutes until they're golden brown and crispy. Baking time may vary due to different ovens and altitudes.
Voila! You've got yourself a mouth-watering side dish that'll have everyone coming back for seconds.
if you want to serve it later, cover potatoes with aluminum foil and keep in a warm oven (let the oven cool a bit, it should not be less than 400 degrees Fahrenheit) until ready to serve.