Step 1: Make the Chocolate Cookies

1. Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
2. In a large bowl, cream together butter, granulated sugar, and brown sugar until light and fluffy.
3. Add eggs and vanilla extract, mixing until well combined.
4. In a separate bowl, whisk together flour, cocoa powder, baking soda, and salt.
5. Slowly add the dry ingredients to the wet mixture, mixing until combined.
6. Stir in the melted semisweet chocolate to create a rich, fudgy dough.
7. Scoop large 2-tablespoon-sized dough balls onto the baking sheet, spacing them 2 inches apart.
8. Bake for 10-12 minutes until set but still soft in the center. Let cool completely before frosting.

Step 2: Make the Chocolate Buttercream

1. In a mixing bowl, beat butter until smooth and creamy.
2. Slowly add powdered sugar and cocoa powder, mixing on low speed.
3. Add heavy cream, vanilla extract, and a pinch of salt, then beat on high speed for 2 minutes until fluffy.

Step 3: Assemble the Cookies

1. Using a piping bag (or a spoon), swirl chocolate buttercream onto the cooled cookies.
2. Sprinkle with chocolate sprinkles or mini chocolate chips for extra texture.
3. Let the frosting set for a few minutes, then enjoy!