Pour the very hot water into a small bowl or heatproof measuring cup. Add the instant coffee and vanilla extract, stir until dissolved to make a concentrated coffee base.
Stir the chocolate and caramel syrups into the coffee base. Whisk briskly until the syrups are fully blended and the mixture is smooth and glossy.
Warm the milk separately: heat gently on the stovetop over low heat or microwave in 30-second bursts until steaming but not boiling. If you like foam, whisk vigorously or froth with a handheld frother for about 20 seconds.
Divide the chocolate-caramel coffee concentrate between two warmed mugs. Slowly pour the warm milk over the concentrate, holding back foam with a spoon and then spooning foam on top.
Finish each latte with an optional swirl of whipped cream, a drizzle of extra caramel, and a sprinkle of toffee bits or chopped nuts for crunch.
Serve immediately while hot. If preparing ahead, keep the concentrate and milk separate and combine just before serving for best texture.