Making the Chocolate Pie Filling:

1. Melt the chocolate: In a small saucepan over low heat, combine the semi-sweet chocolate chips, heavy cream, and butter. Stir constantly until smooth and melted.

2. Add vanilla: Once the chocolate is fully melted, remove from heat and stir in the vanilla extract. Allow the filling to cool slightly before using it in the cookies. The filling should be thick but still spreadable.

Preparing the Cookie Dough:

1. Mix the dry ingredients: In a medium bowl, whisk together the flour, cocoa powder, baking soda, and salt. Set aside.

2. Cream the butter and sugars: In a large bowl, beat the softened butter, brown sugar, and granulated sugar with an electric mixer on medium speed until light and fluffy (about 3-4 minutes).

3. Add egg and vanilla: Add the egg and vanilla extract to the butter mixture and beat until well combined.

4. Combine wet and dry ingredients: Gradually add the dry ingredients to the wet mixture and stir until just combined. Fold in the chocolate chips.

Assembling the Cookies:

1. Preheat the oven: Preheat your oven to 350°F (175°C) and line a baking sheet with parchment paper or a silicone baking mat.

2. Scoop and flatten the dough: Use a tablespoon or cookie scoop to portion out the cookie dough onto the baking sheet. Gently flatten each dough ball with the back of a spoon.

3. Add chocolate filling: Place a spoonful of the chocolate pie filling in the center of each flattened cookie dough ball. Top with a little more dough and seal the filling inside, forming the dough back into a ball.

4. Bake the cookies: Bake for 10-12 minutes, or until the edges are set but the centers are still soft. Let the cookies cool for a few minutes on the baking sheet before transferring them to a wire rack to cool completely