For the whipped cream: In a large bowl or in the bowl of a stand mixer fitted with the whisk attachment, add the cream and whip until it holds soft peaks. Add the sugar and continue to whip until it holds firm peaks.
For the pumpkin spice mocha: Into a small saucepan over medium-low heat, add the pumpkin puree, cocoa powder, granulated sugar, pumpkin pie spice, vanilla and 1 cup water. Stir until melted together to form a thick chocolate syrup, 1 to 2 minutes.
Add 1/2 cup of the chocolate syrup to a large (2-cup) coffee mug. Add 2 shots of espresso and 1 cup of the hot milk and stir to combine. Repeat with the remaining ingredients and 3 more mugs. Top with dollops of whipped cream, a sprinkle of pumpkin pie spice and a pinch of flaky salt if using.