Crème mousseline is essentially a crème pat, but at the end you just add butter and incorporate in one of two ways. This makes a great velvety filling for tarts, Swiss rolls or meringue roulades. You can also pipe it on to a chilled dessert for décor or just eat it with a spoon/take a bath in it. Some people like to flavour their crème mousseline with things like alcohol, praline paste, coffee or caramel.
Dear reader, please use the ingredients listing and method below when making the Crème mousseline recipe on page 34 of The Pastry Chef’s Guide:
Makes about 750 g/1 lb 101/2 oz
500 ml/17 fl oz/2 cups plus 2 tbsp whole milk
1 vanilla pod (bean), split lengthways
125 g/41/2 oz/generous 2/3 cup caster (superfine) sugar 40 g/11/2 oz/generous 1/3 cup cornflour (cornstarch)
6 egg yolks (ideally 20 g/3/4 oz each)
250g softened butter
Stir together the milk with the vanilla pod and half of the sugar in a saucepan and place over a medium heat.
Mix the rest of the sugar with the cornflour, then whisk this into the egg yolks by hand until pale and slightly fluffy.
When the milk is steaming hot and just about to come to the boil (do not let it boil), pour a quarter of the hot liquid over the yolks and whisk thoroughly. Add the rest of the milk in quarters, whisking well after each addition.
Pour the mixture back into the pan over a medium heat and stir with the whisk for about 3 minutes until it starts thicken. Once it starts to thicken, whisk faster until it starts bubbling and then whisk the bubbling custard over the heat for at least 1–2 minutes until nicely thickened. If you feel it’s getting too near to boiling at any point, then just take off the heat for a moment and continue whisking.
Remove the vanilla pod and remove the custard from the heat. Pour/scrape into a bowl or onto a tray so it cools faster. Cover the surface of the custard directly with clingfilm (plastic wrap) to stop it from forming a skin as it cools. Once cool, refrigerate until ready to use.
If it’s a bit lumpy or split, then use a hand blender to knock out those lumps.
Next, either add the softened butter while the custard is still warm and mix it in so it melts. Leave to cool, covered directly with clingfilm (plastic wrap), and then refrigerate preferably overnight or until well chilled. Briefly whisk the chilled mixture in a stand mixer or with a hand-held electric whisk until lightly whipped.
Your other option, which is sometimes slightly riskier because it’s more likely to split, is to cool your crème pât first and then whip it in a machine whilst gradually throwing in the softened butter.
The above recipe is from Ravneet Gill’s The Pastry Chef’s Guide