Cut the large potatoes in half. You can leave the really small ones whole. Place in a lightly greased 6-quart slow cooker.: As you halve the larger potatoes , notice the smooth, waxy texture of the skin and the pale yellow flesh inside. The goal is uniform size so pieces cook at the same rate, which produces consistent tenderness throughout. If pieces are uneven, some may become mushy while others remain firm, so take a moment to match sizes. A common mistake is leaving very large chunks, which extend cooking time and break the rhythm of the recipe.
Sprinkle seasonings and Parmesan cheese over potatoes.: When you set the halved and whole potatoes into the greased slow cooker, you should hear a soft clink as they nestle together. The light grease prevents sticking and encourages even heat distribution across the surface. Make sure the cooker is large enough to hold the potatoes in a single layer with a little room to breathe, because overcrowding can lead to uneven cooking and some soggy pieces.
Mix together butter, oil, and garlic and pour over potatoes.: As you dust the potatoes with the dried herbs, salt, pepper, and parmesan , inhale the combined aroma of herbaceous and cheesy notes. The seasoning layer adheres to the slightly oily surface, creating concentrated pockets of flavor. A common oversight is under seasoning, which leaves the final dish flat, so be mindful to distribute evenly and taste for balance before cooking if you can.
Place lid on slow cooker and cook on HIGH for 3 hours or on LOW for 5 to 6 hours.: When you whisk melted butter with olive oil and minced garlic , the mixture should glisten and carry the scent of fresh garlic . Pouring this over the potatoes coats them in fat that will carry flavor and prevent drying throughout the long cook. The sizzling aroma as the warm fat hits cooler potatoes is reassuring. Avoid pouring boiling butter directly; too hot a fat can shock delicate pieces and break them down prematurely.
Sprinkle with parsley and additional parmesan and serve.: As the slow cooker hums, steam will gently rise and circulate, softening the potatoes while the fats and cheese penetrate. On HIGH you should check near the 2 hour and 45 minute mark for tenderness, testing with a fork; on LOW start testing after 4 hours. You are looking for a fork to glide in easily, signaling a creamy interior. Overcooking can make them collapse into mush, while undercooking leaves a chalky center, so timing based on size is important.
Sprinkle with parsley and additional parmesan and serve: When you remove the lid, expect a warm, cheesy aroma and a glossy sheen on the potatoes . The final sprinkle of fresh chopped parsley adds a green note and a pleasant color contrast, while extra grated parmesan sharpens the savory finish. Serve while hot for the best texture. A common serving mistake is letting the dish sit uncovered for too long, which cools and dulls the flavors quickly.