Wipe down a large glass or metal mixing bowl with lemon juice or vinegar. Add egg whites, then cover and refrigerate for 24 hours. Bring to room temperature.

Line 3 large baking sheets with parchment paper. Set aside.

Add cream of tartar and extract (if desired) to egg whites. Using a stand mixer with a whisk attachment, beat together on medium speed for 2–3 minutes, until very soft peaks form. Stop beating, add about 1⁄3 of the superfine sugar then beat on medium- high speed for 5 seconds. While mixer continues to run, add another 1⁄3 of the sugar, wait 5 seconds, then add the remaining sugar and continue to beat until stiff glossy peaks form.

Sift the almond flour and powdered sugar together in a large glass or metal mixing bowl. Use a spoon to help work any larger pieces through the sieve.

Slowly fold the beaten egg whites into the almond flour mixture in
3 separate additions, folding until combined before adding the next addition. After adding all of the egg whites, pay very close attention to the consistency of the batter. Continue folding until it thins out into the consistency of honey.

Perform the figure 8 test: let the macaron batter fall off your spatula
in the form of a figure 8. The figure 8 should take no more than 10 seconds to sink back into the batter. If it takes less time, your batter was overmixed and
is too thin. If it takes longer, continue slowly folding the batter to deflate more air, then perform the figure 8 test again. It’s best to go very slowly so you don’t accidentally overmix.

Spoon the macaron batter into a piping bag fitted with a medium round
piping tip. Holding the piping bag at a 90 degree angle over the baking sheet, pipe batter into 11⁄2–2-inch rounds about 1–2 inches apart. Bang the pan on the counter a couple of times until the piped macaron batter flattens out and any air bubbles pop. Dust piped macarons with sifted chai mix then let sit out until they are dry and no longer tacky on top, about 30–60 minutes.

Preheat oven to 325°F.

Bake macaron shells for 13 minutes, or until they don’t move when touched. As they bake, they will form the classic “foot.” Let shells cool on the baking sheet for 15–20 minutes, then transfer to a cooling rack.

While the shells are cooling, make
the buttercream. Use a stand mixer with the whisk attachment to whip butter and powdered sugar together on medium-high speed until fluffy. Add caramel cream and continue beating until well incorporated.

Transfer buttercream into a piping bag with a medium round tip. Once macaron shells are completely cool, pipe the filling onto half of the shells and top with remaining shells.

Cover and refrigerate 12–24 hours so the macarons and flavors can mature. Bring to room temperature before serving. Cover leftover macarons and refrigerate for up to 5 days.