In a microwave safe bowl, heat the cream in the microwave until boiling, about 1 1/2 minutes. Remove from the microwave and immediately add in the chocolate chips, salt, and vanilla to the hot cream. Let the mixture sit for 2-3 minutes, and then whisk together until the chocolate is completely incorporated and the mixture is smooth.
This mixture needs to cool completely, which will take at least at hour at room temperature. Set aside while you make the cookies.
Preheat your oven to 350 degrees, and line two large baking sheets with parchment paper. Set aside.
In a large mixing bowl, beat together the butter and sugar until light and fluffy. This will be a little more work than normal because of the cold butter, and I recommend using a stand mixer, or an electric hand mixer. Doing it by hand will be difficult.
Beat in the vanilla extract and eggs until combined. Add in the flour, salt, and baking powder, and beat until a dough forms. It will be fairly firm, and you want to beat it for several minutes to ensure that all the flour is completely incorporated.
Take about half of your dough, and form it into a ball on a floured surface. Place the other half of the dough into the fridge (in the mixing bowl is fine). Roll out the dough until it is about 1/4 inch thick, and then cut into 1 1/2 inch rounds (or your desired shape). Place the cut cookies onto your prepared pans. These don't spread while baking, so you can place them pretty close together.
Bake cookies for 8-10 minutes, or until they are just starting to become golden on the edges. Don't overbake these ones- you want them to stay soft! Continue with the remaining dough until all the cookies are baked. Cool completely.
Once your filling is completely cooled, beat the mixture for several minutes until it has lightened in color and become fluffy. If you overmix it, or if the mixture starts to become too firm while you are filling the cookies as it sets, you can microwave it for 5-10 seconds, and then repeat the whipping process.
Pipe the filling onto your cookies with a star-tipped bag, or simply spread it, and sandwich another cookie on top, pressing gently to seal. Allow the cookies to set for about 30 minutes, and then enjoy!