Into a pressure cooker, add Russet Potato (1.5 pound) and Water (6 quart). Cook for 20 minutes on the Bean/Chili setting. Drain.
Preheat oven to 425 degrees F (218 degrees C).
Into the bowl of a stand mixer, add the potatoes. Mix on low, slowly increasing the speed as you add the Butter (2 tablespoon).
Add Grated Parmesan Cheese (1/4 cup), Ground Black Pepper (2 teaspoon), Kosher Salt (1 1/2 teaspoon), and Ground Coriander (1/4 teaspoon). Mix until well-combined.
Add yolk of the Egg (2). Mix to combine.
Add Buttermilk (1/4 cup). Mix well.
Transfer mixture to a pastry bag fitted with a Wilton number 2D decorating tip. Pipe small mounds onto a baking tray lined with parchment paper. Spray with oil or brush with butter.
Bake for 15-20 minutes, or until golden brown.
Sprinkle with additional salt and pepper. Serve and enjoy!