01 - Preheat oven to 350°F. Line two baking sheets with parchment paper to prevent sticking and ensure easy cleanup.
02 - In a large mixing bowl, beat softened butter and granulated sugar together with an electric mixer until the mixture appears pale, light, and fluffy, approximately 3 to 4 minutes. Blend in vanilla extract until fully incorporated.
03 - Add flour and salt to the butter mixture. Mix on low speed just until a soft dough comes together and no dry flour patches remain. Avoid overmixing to prevent tough cookies.
04 - Portion dough into 1-inch balls. Arrange on prepared baking sheets, leaving 2 inches of space between each ball. Gently press each ball flat with the palm of your hand or the flat bottom of a drinking glass until approximately 1/2 inch thick.
05 - Bake cookies in the preheated oven for 12 to 15 minutes, watching carefully. Remove when edges turn light golden brown while centers remain slightly pale. Transfer cookies to a wire cooling rack and let cool completely before proceeding.
06 - Spread 1 to 2 teaspoons of caramel sauce over the surface of each cooled cookie. Sprinkle with sea salt if using. Place cookies in the refrigerator for 30 minutes to firm the caramel layer.
07 - Set up a double boiler by placing a heatproof bowl over a saucepan of simmering water. Add chopped milk chocolate and butter to the bowl. Stir continuously until completely melted and smooth, then remove from heat.
08 - Spoon or spread the melted chocolate mixture over the caramel layer on each cookie, creating an even topping. Work quickly before chocolate begins to set.
09 - Return cookies to the refrigerator for 15 minutes to allow the chocolate to fully set. Remove from refrigeration and let stand at room temperature for 10 minutes before serving for best texture and flavor.