Starting at the wide end, roll the dough up around the apples, tucking in the sides as you go so the apples are mostly enclosed. It doesn’t need to be perfect—rustic is fine.
Arrange the wrapped dumplings in a single snug layer in the bottom of the slow cooker, seam side down if possible. They can touch and crowd together a bit; that helps them stay soft in the sauce while the tops get a little golden.
In a small bowl or measuring cup, whisk together the melted butter and brown sugar until you have a thick, grainy syrup. It will look a little sandy, and that’s okay.
Pour the butter–brown sugar mixture evenly over the dumplings in the slow cooker, making sure each dumpling gets some of the mixture. It will melt down into a caramel-like sauce as it cooks.
Cover the slow cooker with the lid and cook on HIGH for 2 to 2 1/2 hours, or on LOW for 4 to 4 1/2 hours. The dumplings are done when the dough is cooked through and puffed, the tops are golden, and the sauce is bubbling and thickened around them.
Once cooked, turn the slow cooker to WARM and let the dumplings sit with the lid off for about 10 minutes to let the sauce thicken slightly and the tops set. This is when the edges get that perfect mix of soft and a little crispy.
Spoon the warm dumplings into bowls, making sure to scoop up plenty of the sticky caramel-like sauce from the bottom of the slow cooker. Serve immediately for the best texture.
