For macarons: Heat oven to 300 degrees. Line 2 baking sheets with silicone baking mats or parchment paper. Fit a large pastry bag with a 1/4” round tip. Set a second pastry bag for buttercream aside. Add powdered sugar, almond flour, and Golden Milk Chai Spice to a large food processor (or a smaller one in batches) and pulse for 20 seconds. Add almond flour mixture to a sifter and sift 3 times, going back and forth between two mixing bowls and pushing all of the mixture through the sieve with a rubber spatula each time.
Add egg whites to the bowl of a stand mixer with the whisk attachment and mix on medium-low, adding cream of tartar when egg whites begin to foam. Turn mixing speed up to medium and slowly add granulated sugar when egg whites are opaque, about 2 to 3 min. into mixing. Continue mixing until you just begin to reach glossy and stiff but still flexible peaks. Add half of the sifted dry ingredients to whipped egg whites and fold in gently with rubber spatula. Add second half of the dry ingredients and continue to fold until batter flows like lava without breaking when spatula is raised.
Add batter to pastry bag, leaving enough room at the top to twist the bag and trap batter. Pipe identical 1” rounds, leaving 1 1/2” spaces between each cookie. When finished piping, immediately lift baking sheet out in front of you with straight arms and drop flat onto the counter. Repeat twice more to bring any air bubbles to the surface. Use toothpick to pop any visible air bubbles. Leave piped cookies on the counter uncovered for 20 to 30 min., or until a skin forms and they are no longer sticky to the touch. Bake for 13 to 14 min., or until they release easily from the pan in one piece. Tops should not brown. Let cool for 2 to 3 min. before transferring to wire rack to finish cooling.
For buttercream: In the bowl of a stand mixer fitted with the paddle attachment, beat cream cheese and butter on medium-high for 2 min. or until well-combined and fluffy. Add vanilla of choice and a generous pinch of salt. Stop mixer, add powdered sugar (sifting to break up clumps, if necessary), and start mixer on low until powdered sugar is incorporated. Return mixer to medium-high and beat for 2 min. or until smooth and aerated. Remove bowl from stand mixer and using a rubber spatula, add cookie butter in small dollops, gently folding into buttercream just enough to create clearly-defined swirls. Add buttercream to pastry bag.
To assemble: Pipe a generous layer of buttercream onto bottoms of half the cookies and top with other half to make sandwiches.