1-First Step: Gather all ingredients for mise en place. Soften butter to room temperature. Measure dry items into one bowl, wet into another. Hot water should steam lightly. This setup cuts errors and speeds mixing.

2-Second Step: In large bowl, beat ½ cup butter and 1 cup sugar with electric mixer on medium 3 minutes until light and fluffy. Scrape sides often. This incorporates air for soft texture. Add 1 egg and 1 tsp vanilla; beat 1 minute more until smooth.

3-Third Step: Whisk together 2 cups flour, ½ cup cocoa powder, 1 tsp baking soda, and 1 tsp salt in separate bowl. Alternate adding dry mix and 1 cup buttermilk to butter mixture, starting and ending with dry. Beat low speed to avoid gluten development. Batter will be thin.

4-Fourth Step: Stir in 1 cup hot water until just combined. Batter resembles pancake mix. Do not overmix; lumps are fine. Let rest 10 minutes for flavors to meld. Cover and chill 30 minutes if spreading concerns you.

5-Fifth Step: Scoop ¼-cup mounds batter onto prepared sheets, spacing 3 inches apart. Smooth tops gently with wet spoon for even rounds 2-3 inches wide. Bake one sheet at a time, middle rack, 10-12 minutes. Centers spring back when touched; edges firm but soft. Rotate halfway for even browning. Cool on sheet 5 minutes, then transfer to rack fully.

6-Sixth Step: Repeat with remaining batter. Yields 24-30 cookies. Cool completely, 30 minutes minimum. Flat bottoms ideal for sandwiching. If domed, gently press flat once warm.

7-Seventh Step: Beat 1 cup softened unsalted butter medium speed 2 minutes until creamy. Gradually add 2 cups sifted powdered sugar, ½ cup at a time, beating well after each. Scrape bowl frequently for even texture.

8-Eighth Step: Mix in ½ cup salted caramel sauce, 2 tsp vanilla, and pinch salt. Whip high speed 3-5 minutes for airy fluff. Add 1-2 tbsp heavy cream if too thick. Taste; adjust salt for balance. Frosting pipes smoothly, holds shape.

9-Final Step: Pair cookies by size, flat sides up. Pipe or spread 2-3 tbsp frosting on one, top with matching cookie. Press gently. Roll edges in sprinkles optional. Serve immediately or chill 30 minutes to set. Store as below. Enjoy with milk or coffee. Total time: 1 hour active, 2 hours total including cooling.