Preheat and Prep: Heat your oven to 350°F. Spray the 9-inch pie dish generously—bottom and sides.
Make the crust: In a large microwave-safe bowl, melt the butter for about 1 minute on high. Let it cool briefly, then whisk in the egg, brown sugar, and vanilla until smooth and glossy. Add the flour and salt, stirring just until combined. The batter will be thick and slightly sticky. Spread it into the prepared dish and smooth the top with a spatula.
Par-Bake: Bake for 10-12 minutes. The edges will be firm; the center will look puffy and underdone—that's exactly what you want.
Layer the fillings: Remove from the oven. Sprinkle ¾ cup chocolate chips over the warm crust. Scatter the 1½ cups coconut on top—don't pack it. Drizzle the sweetened condensed milk over everything, covering most of the coconut. Finish with a generous drizzle of salted caramel sauce.
Bake again: Return the pie to the oven for another 25 minutes. Watch carefully during the last 10 minutes—the edges should bubble and the coconut should turn deep golden brown. The center will still have a slight wobble; it firms up as it cools.
Make the drizzle: While the pie cools on a wire rack, melt the remaining ¾ cup chocolate chips in a small bowl—1 minute on high, then stir and heat in 10-second bursts until smooth.
Drizzle and set: Dip a spoon into the melted chocolate and drizzle back and forth across the pie in parallel lines about ½ inch apart. Or use a pastry bag or zip-top bag with a corner cut off. Let the pie cool completely on the rack—at least 4 hours, but overnight is best. This allows the chocolate to set and the caramel to become perfectly sliceable.