Substituting instant imitation flavored pudding mix and cake mix in Bundt Cake recipe

Nothing Bundt Cakes makes delicious dark chocolate and white chocolate with a raspberry center. Thrilled to find copycat recipes online, both call for imitation flavored pudding mixes and cake mixes. Can I use a similar recipe for very rich (with sour cream and butter) dark or white chocolate cake from scratch, adding raspberry sauce swirled in the middle? Reading the ingredients of the instant pudding mix, I could add cornstarch, finely chopped dark or white chocolate chips, vanilla flavoring, and anything else?