In a small saucepan, combine the rolled oats, brown sugar, ground cinnamon, and ground nutmeg with 1/4 cup (60 ml) of milk.
Heat the mixture over medium heat, stirring frequently, until the oats soften and the mixture thickens slightly, about 3 to 4 minutes.
Remove from heat and stir in the vanilla extract and maple syrup.
Brew one shot of espresso and pour it into a large mug.
In a separate container, steam or heat the remaining 1/4 cup (60 ml) of milk until hot and frothy.
Strain the oat mixture through a fine mesh sieve into the mug with espresso, pressing gently to extract the oat flavor but leaving the oats behind.
Add the steamed milk to the mug and stir to combine.
Whip the heavy cream until soft peaks form and gently float it on top of the latte.
Top with whipped cream if desired and sprinkle with a pinch of ground cinnamon for garnish.
Serve immediately and enjoy your oatmeal cookie latte.