Step 1: Make the Chocolate Cookie Dough

1. Preheat oven to 350°F (175°C). Line a baking sheet with parchment paper.
2. In a bowl, whisk together flour, cocoa powder, baking soda, and salt.
3. In another bowl, beat butter, granulated sugar, and brown sugar until light and fluffy.
4. Add egg and vanilla, mixing until combined.
5. Gradually add the dry ingredients, alternating with milk, mixing until a soft dough forms.

Step 2: Bake the Cookies

1. Roll dough into 1-inch balls and place them 2 inches apart on the baking sheet.
2. Flatten slightly with your hand or a spoon.
3. Bake for 8-10 minutes, until the edges are set but the centers are still soft.
4. Let cool on the baking sheet for 5 minutes, then transfer to a wire rack.

Step 3: Make the Raspberry Filling

1. In a small bowl, mix raspberry jam and lemon juice (if using).

Step 4: Make the Optional Chocolate Ganache

1. Heat heavy cream until steaming (not boiling).
2. Pour over chocolate chips, let sit for 2 minutes, then stir until smooth.

Step 5: Assemble the Sandwich Cookies

1. Spread ½ teaspoon raspberry jam onto the flat side of half the cookies.
2. If using, spread a thin layer of ganache on the other half.
3. Sandwich the cookies together and press gently.

Step 6: Decorate & Serve

1. Dust with powdered sugar or drizzle with melted chocolate.
2. Let set for 10 minutes, then enjoy!