Generously coat your 6-quart slow cooker with non-stick cooking spray. This simple step prevents sticking and makes serving and cleanup significantly easier.
Open both cans of peaches and pour the entire contents (fruit and syrup) into the bottom of the prepared slow cooker. Spread them evenly to create a uniform base layer. If using the optional vanilla extract, drizzle it over the peaches now.
Evenly distribute the dry cake mix over the peaches, covering them completely. For best results, resist the urge to stir. If adding cinnamon or nutmeg, sprinkle it over the cake mix at this stage.
Arrange the thinly sliced butter pieces across the top of the cake mix, trying to cover as much surface area as possible. If using nuts, sprinkle them over the butter layer now.
Cover the slow cooker and cook on LOW for 2.5 to 3 hours or on HIGH for 1.5 to 2 hours. The cake is ready when the top appears set and golden brown around the edges, and a toothpick inserted into the cake portion comes out with moist crumbs.
Once cooked, turn off the slow cooker but leave the lid slightly ajar for about 10 minutes. This allows excess moisture to escape and helps the top layer develop a slightly firmer texture while the filling settles.
Serve warm with optional toppings like vanilla ice cream, whipped cream, or a dusting of powdered sugar.