Start by pulling one or two shots of espresso, or brewing a strong dark-roast coffee if you don't own a machine. I keep the coffee on the stronger side so it doesn't get lost under the caramel and chocolate later. Pour it straight into your mug and set it aside while you work on the milk.
Spoon the salted caramel sauce right into the bottom of your mug with the espresso, then stir until it's fully dissolved. I like doing this step before the milk goes in so the caramel doesn't clump. This little trick keeps every sip evenly flavored instead of caramel pooling at the bottom.
In a small saucepan over low-medium heat, whisk together your milk, cocoa powder, and sugar. Keep stirring until it's smooth and just starting to simmer, with no lumps of cocoa left behind. This usually takes me about three to four minutes in a gentle heat.
Once the milk mixture is hot, use a frother or whisk it vigorously to build up some foam. You can also shake it in a sealed jar if you don't have a frother handy. This is what gives your homemade mocha that coffeehouse-style top layer.
Pour the frothed milk mixture into your mug with the coffee and caramel, stirring gently as you go. Top with whipped cream if you're using it, then finish with a drizzle of extra caramel sauce and a pinch of flaky sea salt. Serve it right away while it's warm and the foam is still holding.