Preheat oven to 350 degrees Fahrenheit and line cookie sheets with nonstick baking mats or lightly spray with nonstick baking spray.
In the bowl of an electric mixer, cream together softened butter and granulated sugar. Add vanilla and egg and cream together.
In a separate bowl, whisk together baking cocoa, salt, flour, and baking soda. Add flour mixture to wet mixture and mix just until combined.
Using a Tablespoon measure, scoop cookie dough into the Tablespoon with a flat top, remove from the Tablespoon, form into balls, and place at least 1 1/2" apart on prepared cookie sheets. Press a 1/2 teaspoon measure into the center of each dough ball to make indentations. Use your hands to fix and smooth any cracks, if desired.
Bake for approximately 8 to 9 minutes.
Remove from the oven and immediately press a frozen chocolate into the center of each. Next, quickly remove the cookies from the hot cookie sheet onto a cooling rack. Place the cooling racks in the refrigerator to prevent the chocolates on top from melting. Once the cookies are no longer hot/warm, remove them from the refrigerator and store at room temperature.