Peel and cube the potatoes into roughly 1 1/2-inch pieces. Try to keep the sizes consistent so they cook evenly. Place them in the slow cooker insert.

Scatter the butter pieces over the potatoes, then pour the chicken broth around the edges. Sprinkle in the salt and pepper. Give everything a quick stir so the broth settles to the bottom. The potatoes do not need to be fully covered by liquid. They will steam and soften from the moisture trapped by the lid.

Place the lid on the slow cooker and cook on HIGH for 3 1/2 to 4 hours. Start checking at the 3-hour mark by pressing a potato cube with a fork. It should fall apart with almost no pressure. If there is still resistance, cover and cook another 30 minutes.

About 10 minutes before mashing, warm the heavy cream in a small saucepan over low heat until it is just steaming. Do not let it boil. Adding cold cream to hot potatoes makes them stiff and unevenly textured.

Pour the warm cream over the cooked potatoes. Use a potato masher for a chunky, rustic texture or a hand mixer on low speed for something smoother. Mash or mix only until combined. Overmixing Yukons, even in the slow cooker, can make them gluey if you overwork the starch.

Taste and adjust salt and pepper. If the potatoes feel too thick, add a splash more warm cream or broth. Switch the slow cooker to the LOW or WARM setting. They will hold beautifully for up to 2 hours before serving. Top with chives just before bringing to the table.