Mix and bake according to package directions in 2 round cake pans.
Cool. Slice one chocolate cake and 1 white cake in half horizontally. Freeze 1/2 of the chocolate cake and 1-1/2 of the white cake for future use.
Filling: Beat cream cheese and sugar till smooth. Add cream and whip till firm. Add Bailey's and coffee. Whip till incorporated.
Assembly: Brush whole chocolate layer with 1/4 C. Bailey's. Spread with 1/2 of the filling (1/2" thick). Place the 1/2 white layer on top. Brush with 1/4 C. Bailey's and spread remaining filling. Top with chocolate 1/2 layer. Press to firm and refrigerate while making butter cream.
Butter cream: Cream butter and powdered sugar till light. Beat melted chocolate chips into butter mixture. Continue to cream adding Bailey's till incorporated. Spread onto chilled cake. Decorate as desired. Chill until served.