Prep the slow cooker: Grease the inside of a 5- to 6-quart slow cooker with butter or nonstick spray.
For easier serving, line the bottom with a parchment sling.
Make the cobbler base: In a bowl, whisk flour, granulated sugar, baking powder, and salt. Stir in milk, melted butter, and vanilla until smooth. Spread the batter evenly in the slow cooker.
It will be a thin layer—this is right.
Mix the pecan pie layer: In another bowl, combine chopped pecans, brown sugar, corn syrup, melted butter, beaten eggs, vanilla, cinnamon, and a pinch of salt. Stir until glossy and well blended.
Add the pecan layer: Spoon the pecan mixture gently over the cobbler batter. Don’t stir them together.
Sprinkle pecan halves over the top for a pretty finish.
Create the sauce: Dissolve 2 tablespoons brown sugar in 1 cup hot water. Carefully pour this over the top—again, don’t stir. It will look like too much liquid.
That’s what forms the caramel sauce as it cooks.
Cook low and slow: Cover and cook on Low for 2.5 to 3.5 hours, or until the edges are set and the center is mostly set but still a little jiggly and glossy. Avoid opening the lid for the first 2 hours.
Rest before serving: Turn off the slow cooker and let the cobbler sit, covered, for 15–20 minutes. This helps the sauce thicken.
Serve warm: Scoop into bowls, making sure to get both the cake and the sauce.
Top with vanilla ice cream or whipped cream, and a light sprinkle of flaky salt if you like.