Prepare the Potatoes: Peel and dice the russet potatoes into even chunks. Place them in a large pot and cover with cold water. Bring to a boil over high heat, then reduce to medium-high and cook until the potatoes are fork-tender, approximately 15-20 minutes. Drain thoroughly in a colander.

Create the Base: Transfer the drained potatoes to a large mixing bowl. Add the butter and cream cheese while the potatoes are still hot, allowing them to melt into the mixture. Mix well using a potato masher or electric mixer until smooth and well combined.

Add Flavor Elements: Incorporate the Italian blend cheese, fiesta blend cheese, salt, pepper, and garlic powder into the potato mixture. Mix thoroughly to distribute the flavors evenly throughout the potatoes.

Enrich the Mixture: Add the egg yolks one at a time, mixing well after each addition. These will add richness and help create a beautiful golden crust when baked. Finally, pour in the heavy cream and mix until the consistency is smooth and creamy.

Prepare for Baking: Spread the potato mixture evenly in a 9×13 inch baking dish. Use a fork to create lines or decorative patterns across the top of the potatoes. This will help create more crispy edges when baking.

Bake to Perfection: Place the dish in a preheated 400°F oven and bake for 20 minutes until heated through. Then, switch the oven to broil on high setting and continue cooking for an additional 3-5 minutes, watching carefully until the top becomes crispy and golden brown.