If using chocolate bars, break into squares about 1/2 inch wide; set aside.
Cream butter and sugar until sugar dissolves, about 5 minutes. Add eggs one at a time, beating after each addition. Mix in vanilla.
Mix flour, salt and baking powder together and add in two parts to the batter, mixing after each addition.
Add milk and mix until the batter is as thick as brownie batter (thick, but spreadable). Fold in chocolate bits.
Pour into a buttered 9x5-inch loaf pan. Smooth top. Bake in a preheated 350-degree oven for 50-60 minutes, or until a knife inserted into center of cake comes out clean (it will have melted chocolate on it). Do not overbake or it will be dry.
Let the cake cool completely, then frost it by melting 6 ounces of chocolate bark and spreading it over the top and sides of the cake. Cool and slice.