Set up a double boiler, a small pot with a little bit of water with a glass bowl on top, over low heat. Add the 6 oz chocolate into the glass bowl. Stir frequently with a rubber spoon until just melted. Set to the side to cool down a bit.
In a large bowl, using an electric hand mixer, cream the butter until smooth and creamy. Add in the sugar and mix until light and fluffy.
Add in the eggs and vanilla. Mix until well combined and smooth.
Again using the electric mixer, add the melted chocolate and milk. Mix until well combined.
In a small bowl mix the flour, baking powder, baking soda, salt and cocoa powder together.
Slowly add the dry ingredients to the wet. Mix until just combined. The batter is a little bit on the thicker side, it is not runny.
Divide the batter equally into two buttered cake pans. Bake for approx 25 minutes, or until a toothpick comes out clean. Once the cakes are completely cooled, remove them from their pans and wrap each well with plastic wrap.
For the Caramel Buttercream:
First you have to make a caramel sauce. Once again, set up a double boiler, add the caramels and 1 Tbsp butter. Stirring frequently. Once the caramels have begun to melt add in the 1/3 cup milk. Stir continuously until the caramel is completely melted and all ingredients are incorporated.
Once the caramel is cooled completely you can start making the buttercream frosting. In a large bowl, using an electric mixer, cream the 2 sticks of butter. Add the powdered sugar and slowly incorporate.
Add the caramel sauce (reserving 1 Tbsp to drizzle over top) and 5 Tbsp of milk and mix for several minutes until the buttercream is well combined, light and fluffy.
Place one cake round on a platter. Frost just the top then place the second round directly on top.
Frost the entire cake and don't worry about it looking perfect. Once the cake is covered in the caramel buttercream gently press the crushed pretzels into the frosting. Drizzle the remaining 1 Tbsp of caramel sauce over top the cake.