COOKIES:
Preheat oven to 350 degrees
Line two cookie sheets with parchment, set aside.
Melt 1 1/2 cups of chocolate, stir in the hot water and stir quickly until combined, stir until smooth. Set aside.
In bowl of mixer cream butter and sugar together.
Add in the salt, eggs and vanilla. Mix to combine.
With mixer on medium speed add in the melted chocolate. Keep mixer going until completely combined, scrape down bowl as needed with spatula.
Bring mixer down to low speed, add in flour and baking powder.
Mix until dough is formed, add in remaining chocolate chips, mix.
Scoop Tablespoonfuls onto baking sheet, press to flatten them.
Bake 8-9 minutes. Centers should still seem soft.
Let cool completely.
BUTTERCREAM:
Cream butter
Slowly add in the first half of the powdered sugar (1 cup) with mixer on low, alternating with milk as needed.
Add in the blackberry jam and vanilla, continue mixing.
With mixer on low add in the rest of the powdered sugar (1 cup).
Mix until completely combined.
ASSEMBLY:
Match up cookies in pairs.
Take one cookie from the pair and spoon a dollop of buttercream on it.
Gently press the second cookie on top of butter cream to make a sandwich.
Repeat with remaining cookies.
Keep in a cool place, buttercream is sensitive to warm temps and can become very soft.