Preheat the oven to 350°F. Line a 9x13-inch baking dish with parchment paper, leaving an overhang for easy removal.
In a large bowl, use a hand mixer to cream ¾ cup softened unsalted butter and ½ cup granulated sugar until creamy and light.
Add 1 large egg and ½ teaspoon vanilla extract to the butter mixture and mix until incorporated.
Add 2 cups all-purpose flour and ¼ teaspoon salt to the bowl and mix just until combined; the mixture will be crumbly.
Press the crumbly dough evenly into the bottom of the prepared pan to form the cookie base. Bake for 20–25 minutes, until the edges are lightly golden. Remove from oven and let the crust cool in the pan while you toast the coconut.
Spread 3 cups shredded coconut in a single layer on a baking sheet. Toast in the 350°F oven, tossing occasionally, for 10–15 minutes until slightly golden. Remove and set aside to cool.
Unwrap 12 ounces chewy caramels into a microwave-safe bowl. Add 3 tablespoons whole milk and the remaining ¼ teaspoon salt. Microwave in 30-second intervals, stirring between each, until the caramels are fully melted and the mixture is smooth.
Stir the toasted coconut into the melted caramel until evenly combined. Immediately spread the caramel-coconut mixture evenly over the cooled cookie base. Allow the layered bars to cool completely (room temperature or refrigerated) so the caramel sets.
Use the parchment overhang to lift the set bars from the pan and place on a cutting surface. Cut into squares or your desired shapes.
Put 20 ounces chocolate chips in a microwave-safe bowl and melt in 30-second intervals, stirring well between each interval, until smooth. Dip the bottom of each bar into the melted chocolate, letting excess drip off, and place the chocolate-dipped bars onto a parchment-lined baking sheet.
Put the remaining melted chocolate into a zip-top bag, snip a corner, and pipe lines of chocolate over each square. Refrigerate the bars until the chocolate hardens, then serve.