Add warm heavy cream to the chocolate and let it sit for a few minutes.
Emulsify with an immersion blender.
Add cold heavy cream and emulsify again.
Transfer ganache into a flat container and cover with plastic wrap "to contact".
Refrigerate ganache for 8-12 hours. After that, whip and fill macarons.
How to Make French Macarons
Line two baking sheet pans with a baking mat. Measure all ingredients using a digital kitchen scale. Get all tools ready before starting this recipe.
In the other mixing bowl, sift together almond flour and powdered sugar. You can sift a few times if needed, depending on the almond flour you are using.
Add egg whites to a mixing bowl of a stand mixer. Whisk on low speed. Start adding sugar in a few parts. After that, change the speed in the mixer to medium and set up the timer for 15 minutes. Meringue should be shiny and have stiff peaks.
Add sifted dry ingredients to the French meringue and fold the batter using a spatula. Do not overfold! Check the batter every 5 folds.
The batter is ready when it flows fast from the spatula.
Transfer the batter to the piping bag with a round tip.
Pipe macaron shells on the prepared baking mats. Hold the piping bag straight and apply pressure when you start piping, then stop when you reach the desired size of the macaron shell.
Lightly tap the baking tray to remove air bubbles. Use a toothpick or a baking needle to remove the bubbles from the piped macaron shells. Sprinkle shells with rainbow sprinkles.
Let macaron shells rest (dry) on the countertop for about 15 minutes.
Meanwhile, preheat the oven to 300°F (150 °C).
Bake macaron shells in a preheated oven for 14-16 minutes. Baking time and temperature may be different, depending on your oven.
Remove the baking tray from the oven and let the macaron shells cool to room temperature before removing them from the mat.
Pair macaron shells of similar sizes before filling them.
How to Assemble Birthday Cake Macarons
Whip ganache using a hand mixer.
Add sprinkles and transfer into a pastry bag with a round tip.
Pipe whipped ganache on one flat side of the macaron shell and sandwich with the other shell. Make sure there is no ganache coming out from the sides of the macaron. Repeat with the rest of the macarons.
Place filled macarons in the airtight container and refrigerate for 8-12 hours. Macarons need to "mature" before you can enjoy them. This is an important step; do not skip it.
Video
Notes
Measure all ingredients correctly, using a digital kitchen scale. Do not overwhip ganache.