Gently spoon the batter over the pineapple rings, spreading it out as evenly as you can. Try not to disturb the pineapple too much; it’s fine if a little juice peeks through around the edges.
Cover the slow cooker with the lid. Cook on HIGH for 2 to 2 1/2 hours, or on LOW for 4 to 4 1/2 hours, until the top of the cake is set, the edges are golden-brown, and a toothpick inserted into the cake portion comes out mostly clean.
Once done, turn off the slow cooker and let the cake sit, covered, for 10 to 15 minutes. This rest time helps the juices settle and gives the cake that glossy, slightly caramelized look with a moist, spongy texture.
Serve the cake warm, scooping down through the cake layer to the pineapple rings and syrup underneath. You can serve it straight from the slow cooker for that cozy, rustic feel, or carefully lift out portions with a spatula to keep some of the pineapple rings visible on top.
