Step 1

Chop chocolate up finely and measure out hazelnut butter (make sure it's room temperature) and keep it handy.

Step 2

Place chopped chocolate together with single cream and maple syrup (if using sugar, hold) in a metal or glass bowl suspended over a pot of water. Make sure the bottom of the bowl does not touch the water. Warm up the water on a very low heat (chocolate is very sensitive to overheating, which is why I don't recommend using a microwave to melt it). When the water barely starts to simmer, switch the heat off but keep the bowl on the pot.

Step 3

Once the chocolate looks melted, very gently and slowly stir it into the other ingredient(s). Stir as little as you can (dark chocolate in particular is very sensitive to overstirring).

Step 4

Once incorporated, gently and slowly stir in hazelnut butter. You should end up with a shiny homogenous ganache (SEE NOTES for troubleshooting). Keep the bowl over the warm pot until ready to use.

Step 5

Put aquafaba, lemon juice and salt in a large, spotlessly clean (grease residue inhibits aquafaba from reaching stiff peaks) bowl. Using an electric mixer, whip aquafaba until it reaches stiff peaks - to check turn the bowl upside down and the mixture should not slide. It takes about 5 minutes with a handheld mixer.

Step 6

If using SUGAR (instead of maple syrup), whisk it into the whipped aquafaba at this point, tablespoon by tablespoon, whipping well after each addition so that the sugar melts into the meringue mixture.

Step 7

Wipe the bottom of the bowl with ganache so that water droplets don't end up in your aquafaba and ensure chocolate ganache is just barely warm. Add approximately a third of it to the bowl of aquafaba. Using a slow folding motion, incorporate the ganache into the aquafaba gently. Incorporate the other two thirds in the same manner, being very gentle and slow so that you don't knock too much air out of the aquafaba. The mixture will deflate a fair bit before you are done - that's normal - but it should still be very mousse-y and airy (full of tiny bubbles) when you are done.

Step 8

Pour the mixture into glasses, giving the mixture a gentle stir between each portion. Once in glasses, use a toothpick to gently stir the mixture once more.

Step 9

Set in the fridge overnight (or 8 hours) to set.

Step 10

Decorate and serve. You can make it a day or two ahead but once set, keep in an air-tight container in the fridge or else the mousse will dry out too much.

Step 11

Preheat the oven to 160° C / 320° F and spread hazelnuts on a large baking tray. Bake until fragrant, bursting out of their skins and lightly golden. Start checking after 12 minutes (they usually take about 15 but it depends on how dry the nuts were to begin with).

Step 12

Place warm hazelnuts inside a clean kitchen towel and rub between your hands to loosen up most of the skins. Pick out the hazelnuts and place in a food processor.

Step 13

Process hazelnuts, scraping down the sides from time to time, until they turn into hazelnut butter. In my old Kenwood, it takes about 8 minutes. Transfer to a jar and keep in the fridge.