Roughly break up the chocolate and melt it in a bowl suspended over hot water. Coat it over the tart base, chill and set in the fridge.
For the mousse: Sprinkle the gelatin into the water and leave to soak. Use the bowl in which you melted the chocolate earlier and melt the gelatin mixture and milk jam together whilst suspended over boiling water.
Add the egg whites into a bowl and whip them into a meringue. When you start whisking, add the sugar and keep going until stiff peaks form.
In a separate bowl, whip the cream until stiff peaks form.
Add the whipped ingredients from steps 4 and 5 into the mixture from step 3 and mix lightly. Once everything is combined, pour the mixture onto the tart base and put it in the refigerator.
For the cream: Heat the sweet chestnuts in the microwave for 2 minutes to make them easier to crush. Crush the chestnuts with a masher and mix them with the sugar. Finally add the milk little by little and mix until smooth.
Strain the sweet chestnuts. In a separate bowl, whip some cream until stiff peaks form. Add the strained sweet chestnut mixture.
Once the mousse has set, roughly crush up the sweet chestnuts for decoration alongside the whipped cream intended for decoration.
Pipe the marron cream in swirls and finish decorating with leftover cream and sweet chestnuts.
If you have some cream left over, just put it in a serving dish or container and leave it to set in the fridge. You'll end up with a dessert like this.
Story Behind this Recipe
I wanted to eat mont blanc but the paste is so expensive. I wanted to make a simple yet gorgeous tart that could almost look shop-bought, so I filled this tart with mousse. For the mousse, I used milk jam that I had been given as a souvenir from Europe. The chocolate will prevent the tart from cooling.
The sweet chestnuts I used were on sale. I bought 3 x 90 g bags and used 2 bags for paste and 1 bag for decoration. I don't have a food processor or hand mixer so I used a masher to crush the walnuts. If you have either of these though, feel free to use them instead, it'll make things much easier.