Preheat oven to 350°F. For the cookie base: Line a 9x13 inch baking pan with aluminum foil and spray it lightly with cooking spray.
In a large bowl, cream together sugar and butter until fluffy.
Beat in egg and vanilla extract.
Working at a low speed, gradually beat in flour and salt until mixture is crumbly, like wet sand.
Pour crumbly dough into prepared pan and press into an even layer.
Bake for 20-25 minutes, until base is set and edges are lightly browned. Cool completely on a wire rack.
For the topping, unwrap the caramels and place in a large microwave-safe bowl with milk and salt. Microwave on high for 3-4 minutes, stopping to stir a few times to help the caramel melt.
When smooth, fold in toasted coconut with a spatula.
Put spoonfuls of the topping all over the shortbread base. Using a spatula, spread the topping in an even layer. Let topping set until cooled.
When cooled, cut into 30 bars with a large knife or a pizza cutter.
Once bars are cut, melt chocolate in a small bowl. Heat it on high in the microwave in 45-second intervals, stirring thoroughly to prevent scorching. Dip the base of each bar into the chocolate and place on a clean piece of wax paper.
If desired, use remaining chocolate to drizzle bars with chocolate to finish.
Let chocolate set completely before storing in an airtight container.