In a small saucepan, combine the rolled oats and water. Bring to a simmer over medium heat and cook for 5 minutes, stirring occasionally.
Add the brown sugar, ground cinnamon, and ground nutmeg to the oats. Stir well and cook for another 3 minutes until the mixture thickens slightly.
Remove the saucepan from heat and stir in the vanilla extract. Let the oatmeal cookie syrup cool slightly.
Strain the oatmeal cookie syrup through a fine mesh sieve into a small bowl or cup, pressing the oats to extract as much liquid as possible. Discard the solids.
Brew one shot of espresso using your espresso machine or stovetop espresso maker.
In a small saucepan, heat the milk over medium heat until steaming but not boiling, or use a milk steamer to froth the milk.
Pour the espresso into a large mug. Add the strained oatmeal cookie syrup and maple syrup. Stir to combine.
Pour the steamed milk over the espresso mixture, holding back the foam with a spoon, then spoon the foam on top.
Top the latte with whipped cream and a light dusting of ground cinnamon.
Serve immediately and enjoy your homemade Oatmeal Cookie Latte.