Making the Chocolate Cookies

1. In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. This ensures the dry ingredients are evenly distributed.
2. In a separate large bowl, beat the softened butter, brown sugar, and white sugar together until light and fluffy. This step incorporates air into the mixture, resulting in softer cookies.
3. Add the egg and vanilla extract, mixing until fully combined.
4. With the mixer on low speed, gradually add the dry ingredients to the butter mixture. Mix until a dough forms. The dough will be sticky at this stage.
5. Stir in the chocolate chips, ensuring they are evenly distributed throughout the dough.
6. Cover the bowl with plastic wrap and refrigerate the dough for at least 3 hours or overnight. Chilling the dough prevents the cookies from spreading too much during baking.
7. Preheat the oven to 350°F and line baking sheets with parchment paper or silicone baking mats.
8. Form the dough into balls, about 1 to 1.5 tablespoons in size, and place them two inches apart on the prepared baking sheets.
9. Bake for 8-10 minutes, or until the tops of the cookies appear set. They may look slightly underbaked, but they will continue to firm up as they cool.
10. Allow the cookies to cool on the baking sheet for a few minutes before transferring them to a wire rack to cool completely.

Making the Raspberry Cream Cheese Frosting

1. Blend the raspberries in a food processor or blender until smooth.
2. Strain the raspberry puree through a metal sieve to remove the seeds, using a spoon to press the liquid through.
3. Transfer the seedless puree to a small saucepan and heat over low heat, stirring frequently. Allow it to gently boil until thickened and reduced to a jam-like consistency. This intensifies the raspberry flavor. Let it cool completely before using.
4. In a large bowl, beat the butter until smooth, then add the cream cheese and mix until fully incorporated.
5. Gradually add in 1 cup of powdered sugar and the salt, mixing until smooth.
6. Mix in one tablespoon of the cooled raspberry puree.
7. Add the remaining powdered sugar, ½ cup at a time, and an additional tablespoon of raspberry puree. Adjust the sugar amount based on the desired consistency and sweetness.

Assembling the Sandwich Cookies

1. Once the cookies are completely cool, spread about one tablespoon of raspberry frosting on the bottom side of a cookie.
2. Place another cookie on top, gently pressing to form a sandwich.
3. Repeat with the remaining cookies and frosting.
4. Store the cookies in an airtight container in the refrigerator for up to four days