Peel and quarter the Yukon Gold potatoes, then place them in a large pot and cover with cold water. Season the water generously with salt.
Bring the pot to a boil over medium-high heat and cook the potatoes for about 15 minutes or until fork-tender. Drain well in a colander.
Use a potato ricer to rice the drained potatoes back into the pot.
Add the sliced unsalted butter to the warm riced potatoes and stir until melted and blended.
Add the smoked Gouda, sour cream, and about ⅓ cup of warm heavy cream. Season with salt and pepper, then stir until smooth and creamy. Adjust the consistency with more cream if necessary.
Taste the mashed potatoes and adjust the seasoning if necessary.
Serve the mashed potatoes warm as a side dish.