- To start off with the filling, pour 175g of sugar into a thick-bottomed pot over medium heat. Let the sugar melt to get a nice amber colour. You can stir it, but I prefer letting it melt on its own and swirling the caramel inside the pot until all the sugar is melted. Set aside.
- In another pot, heat up the whipping cream until it's frothy. Pour into the caramel and mix the two together until they're incorporated. Let cool until about 115F, or until you find it won't separate if you add the butter. I basically opened the window and stirred until it thickened a bit. Add 175g of butter, chunk by chunk, mixing until it's completely incorporated. It'll be tepid by the time you're done incorporating all the butter. Cover with plastic wrap (touching the surface of the caramel) so it doesn't form a skin. Set aside.
- For the macaron shells, process almonds with icing sugar until you get a fine powder. Sift into a bowl (you may need to process it multiple times to get all the lumps out) and mix 60g of the egg whites with it until you get a paste. Add brown food colouring until you get a milk chocolate brown. It'll mellow out when you add the meringue. Set aside.
- Whip the remaining 60g egg whites with 35g of sugar until almost stiff peak stage. (See picture below). Meanwhile, heat 150g sugar with 50g water until 230F, then slowly stream the sugar syrup into the meringue with the beater running. Whip the meringue until stiff peak or until the meringue stays inside the beater when you pull it out.
- Add a dollop of the meringue into the almond paste and mix to loosen it up. Then incorporate the remaining meringue, folding until you get a lava-like texture that flows in thick ribbons that'll sink back into the batter within 20-30 seconds.
- Transfer to a piping bag fitted with a Wilton 12 round tip, pipe 1 1/2 inch circles on a parchment-paper lined baking sheet and bake for 12-14 minutes (you'll know it's ready when you touch the domes of the shells in the oven and they don't wobble much).
- Once baked, let cool on a wire rack for about 2 minutes, then gently remove from the baking sheet and let cool completely before filling.
- To finish the buttercream, whip 250g of butter until creamy. Add the caramel and whip until incorporated. Transfer to a piping bag and chill for about 10 minutes for it to be less runny.
- Fill the cookies with a generous dollop of buttercream (about 2 tsp depending on the size of the cookie). Gently squish the matching macaron shell together to get a sandwich of deliciousness.