Prep the crockpot. Line the base and sides of your slow cooker with a sheet of parchment, leaving some overhang for lifting. Lightly grease the parchment. This prevents sticking and makes clean-up easy.

Cream the butter and sugars. In a large bowl, beat softened butter with brown sugar and granulated sugar until light and fluffy, about 2–3 minutes. Use a hand mixer or stand mixer for best results.

Add eggs and vanilla. Mix in the eggs one at a time, then beat in the vanilla until smooth. Scrape the bowl to ensure everything is well combined.

Combine dry ingredients. In a separate bowl, whisk together flour, cornstarch, baking soda, and salt. The cornstarch helps keep the cookie cake ultra-soft.

Bring it together. Add the dry ingredients to the wet in two additions, mixing on low just until the flour disappears. Do not overmix.

Fold in the chocolate. Stir in the chocolate chips (and mini chips or chunks if using). Save a small handful for sprinkling on top.

Press into the crock. Transfer the dough to the lined insert and press into an even layer. Scatter the reserved chips over the surface and gently press them in.

Cook low and slow. Cover and cook on Low for 2 to 3 hours, or until the edges are set and lightly golden and the center looks just a touch underdone. Start checking at the 2-hour mark. Every slow cooker runs a bit differently.

Finish and rest. Turn off the heat. If using, sprinkle a pinch of flaky sea salt on top. Let the cookie cake rest in the crock with the lid off for 20–30 minutes to set before lifting it out with the parchment.

Slice and serve. Cut into wedges or squares. Serve warm as-is or with vanilla ice cream and a drizzle of chocolate or caramel sauce.