Using a stand mixer with the paddle attachment, cream the butter with the sugar and salt. Add in the flour and continue to beat until combined.
Transfer the dough onto a piece of plastic wrap and roll into a log, twisting the ends so that it's tightly wrapped. Chill in the refrigerator for at least 2 hours.
Preheat the oven to 350°F, keeping the dough in the refrigerator until the oven is ready to use. Remove dough from the refrigerator, unwrap, and slice into ½ inch rounds. Arrange cookies on a lined baking sheet and bake for 22-24 minutes. Allow the cookies to cool on the baking sheet for 10 minutes, then transfer to a cooling rack to cool completely before moving on to the next step.
Once the cookies are completely cooled, spoon or pipe dulce de leche onto centers of each cookie, and spread to cover the surface as necessary. Chill cookies in the refrigerator for at least 30 minutes.
In a microwave safe bowl, melt the chocolate candy coating or chocolate chips on 50% power in 30 second intervals, stirring between each interval. Spread a small amount of melted chocolate directly on top of the caramel layer. Allow cookies to set before serving.
Notes
The amount of caramel and chocolate used on each cookie is entirely up to personal preference -- there's virtually no right or wrong amount to use. However, depending on how thick your layers are, you may need more dulce de leche and/or chocolate candy coating than I've specified here.
For me, the recipe yields just about 14 cookies but this can vary based on how thick or thin you slice your cookies.
For perfectly round and uniform cookies, I like to use a round cookie cutter when the cookies are still warm and soft, to further reinforce the round shape. Do not attempt to pull the cut cookies off until they have cooled.