Make the cookie topping (optional). In a small skillet, melt the butter over medium heat. Continue to heat until browned, then stir in the crushed cookies. Continue to cook for another 30 seconds, then remove from heat and set aside.
Make the pistachio cold foam. Add the heavy cream, pistachio syrup, and whole milk to a small glass or container and froth with a milk frother for 15-30 seconds. Set aside.
Add the cold brew coffee to a tall glass, then stir in 1 tablespoon pistachio syrup and 1 teaspoon vanilla syrup. Top with ice.
Pour the cold foam over the sweetened cold brew coffee, then sprinkle with 1 tablespoon of brown butter cookie topping, if desired. Drink up!
Notes
***Cookie Topping: The cookie topping portion of this recipe yields 4 tablespoon of the topping, enough for 4 drinks. Store leftover cookie topping in an airtight container for up to 7 days at room temperature.