First prepare a flat tray and baking paper with circles about 1 1/2″ (4 cm) in diameter drawn on it, if you do not have a special macaron tray. Flip the baking paper over so there's no traces of pencil visible.
The egg whites must be left in the refrigerator for at least 24 hours in advance, in fact it is best to leave them for 3 days. On the day of the preparation, take them out to room temperature for about 2 hours.
The resulting flour needs to be sifted through a sieve, thus removing the larger lumps. It is preferable to use a high metal bowl, in which to whip the egg whites - first on low, then at a higher speed. Gradually add the granulated sugar in 2 lots, increase the speed of the mixer and whip until you get a stiff and shiny snow.
Take the bowl away from the mixer and begin to add the dry ingredients, i.e. the almond flour and powdered sugar – in 3 to 4 lots. Stir the mixture with a large spatula in one direction - from the bottom towards the top. Each time, make about 10 complete rotations, so that the mixture is drawn up.
The total number of rotations needs to be exactly 50. You need to get a shiny mixture like lava, and to check to see if it is ready, take a teaspoon of the mixture and place it in a shallow dish. If it forms a tip that does not disappear in a few seconds, it means you need to stir it a few more times. Transfer the finished mixture into a pastry bag with a nozzle of about 1 1/4″ (3.5 cm).
Spray it on the baking paper with the circles. Hit the bottom of the tray several times onto the counter to expel the air from the egg whites. Leave it aside for 40 minutes to dry. If small tips form on the macarons, you can press on them with slightly moistened fingers until smooth.
Bake at 302°F (150 °C) for about 10 to 15 minutes or 266°F (130 °C) for about 20 minutes. To see if they're ready, check if they can be easily separated from the paper, or when they've formed a nice footing at their base.
Blend the jam slightly to make it smoother and put it on low heat for a few minutes to relax. Remove it from the heat and add cognac or rum. Mix.
Put the gelatin in cold water and once it swells nicely, pour it into the warm jam mixture. Stir and leave it in a cool area to tighten, but not too much, so it can be placed on the macarons. This can be done with a pastry bag or a small teaspoon - smear it well on the top of the macaron. Top with the second macaron.
Leave the macarons to cool for a few hours before consumption. Note: I baked them at 266°F (130 °C) with the fan on for exactly 25 minutes because every oven is different. I worked with great precision in terms of the amounts and I used an electronic kitchen scale, as this is one of the conditions for making good macarons.
Source: I used In the Kitchen with Joanna Petrova and joyofbaking.