Let’s walk through making this exquisite French buttercream step-by-step. Precision and timing are important here, so read through everything first. Begin by placing your five large egg yolks into the clean bowl of your stand mixer fitted with the whisk attachment. Beat them on medium-high speed for several minutes until they become noticeably thick, pale yellow, and have increased in volume. This incorporates air and prepares them to receive the hot syrup.

While the yolks are whipping, combine the water and granulated sugar in your small, heavy-bottomed saucepan. Place it over medium-high heat. Crucially, do not stir the mixture once the sugar starts dissolving. Stirring can cause crystallization. Allow the syrup to come to a boil and continue heating, undisturbed, until your candy thermometer registers exactly 238°F (115°C), the soft-ball stage. This usually takes about 5 minutes but rely on the thermometer, not the timer. Have a bowl of cold water nearby in case you need to stop the cooking quickly by dipping the pan base into it.

As soon as the syrup reaches 238°F/115°C, immediately remove it from the heat. Turn your mixer speed down to medium-low. With the mixer running, very carefully and slowly pour the hot sugar syrup in a thin, steady stream down the side of the mixing bowl into the whipping egg yolks. Avoid pouring it directly onto the whisk, as it can splash or spin threads of hard sugar. Pouring it slowly prevents the yolks from scrambling from the heat shock.

Once all the syrup has been added, increase the mixer speed to high. Continue whisking the pâte à bombe mixture vigorously for about 5 to 7 minutes, or potentially longer depending on your mixer and room temperature. The goal is for the mixture to become very thick, pale, voluminous, and – critically – cooled down to just lukewarm or near room temperature. You must feel the outside of the bowl; it should no longer feel warm. Adding butter to a warm base will result in melted, soupy buttercream. Be patient with this cooling step; it’s essential.

Now, ensure your butter is properly softened – it should be pliable and cool to the touch (around 65-68°F / 18-20°C), not greasy or melted. Switch from the whisk attachment to the paddle attachment on your stand mixer (this helps prevent over-aeration later). With the mixer on medium-low speed, begin adding the softened butter, just one or two tablespoons at a time. Allow each addition to incorporate for about 15-20 seconds before adding the next.

During this stage, the mixture will likely look curdled, separated, or completely wrong – do not panic! This is normal. As you continue adding the butter slowly and beating, the emulsion will start to come together. Keep scraping down the sides and bottom of the bowl frequently to ensure all the butter is incorporating evenly. The buttercream will gradually thicken and become smooth.

Once all the butter has been added and the buttercream looks smooth and cohesive, it’s time for the flavorings. Make sure your melted semi-sweet chocolate has cooled slightly so it doesn’t melt the butter. Add the melted chocolate, salt, and coffee emulsion/extract to the bowl.

Mix again on medium-low speed for another minute or two, just until the chocolate and coffee are fully incorporated, and the buttercream is uniform in color and fluffy. Be careful not to overbeat at this final stage, as it can incorporate too much air, making the buttercream prone to air bubbles when frosting. Your luxurious Chocolate Coffee French Buttercream is now ready to use!