Experimenting Mocha Latte Recipe

I’m opening a cafe and i’m experimenting on mocha lattes since i want to add it to my menu. I came on here to ask for tips. I want to make high quality mocha lattes not just what the offer in starbucks. I used lotte 72% dark chocolate and i find that it doesn’t completely dissolve and blend with the coffee. I pulled the shot on top of the chocolate before adding the milk.

Would really appreciate any tips you guys have. I’m an amateur and the coffee shop i’m opening is small, but i really do enjoy making coffee and want to share it with people from our city.