In a small saucepan, combine the water, rolled oats, brown sugar, ground cinnamon, and ground nutmeg.
Bring the mixture to a simmer over medium heat, stirring occasionally, and cook for 3 to 4 minutes until the oats soften and the sugar dissolves.
Remove the saucepan from heat and strain the oat mixture through a fine mesh sieve into a bowl, pressing gently to extract the liquid. Discard the solids.
Heat the milk in a separate small saucepan or microwave until hot but not boiling.
Froth the hot milk using a milk frother or whisk vigorously until foamy.
Pour the espresso shot into a large mug.
Add the strained oatmeal cookie syrup and vanilla extract to the espresso and stir to combine.
Slowly pour the frothed milk over the espresso mixture, holding back the foam with a spoon.
Spoon the foam on top of the latte.
Top with a dollop of whipped cream and a light sprinkle of ground cinnamon for garnish.
Serve immediately and enjoy your oatmeal cookie latte.