Onyx

Cut the cold butter into small cubes, add it to all the other ingredients and mix them using the flat beater in a stand mixer until a dough forms (however, take care not to knead it).
Shake the dough through a 4mm sieve (or a filter used for washing dishes if you don’t have one) so it forms into evenly sized pieces.
Freeze them before separating them out so they keep a nice shape.
Store in the refrigerator or freezer until you are ready to cook.
Spread the streusel over a baking sheet and bake for approx. 20 minutes at 295°F (145°C) with the vents open until it is golden-brown.

Using a spatula, combine the two ingredients.
Store in a tightly sealed box.

Bring the cream and milk to a boil and combine with the premixed egg yolk-sugar combination.
Thicken the mixture at a temperature of 185°F (85°C), strain through muslin and use immediately.

Hydrate the gelatin in cold water and drain away any excess then, once the crème anglaise is hot, add the gelatin in.
Gradually pour the crème anglaise onto the melted couverture chocolate, stirring it in with a spatula to create a smooth, shiny and elastic texture.
Mix using an immersion blender to obtain a perfect emulsion. Make sure no air bubbles form.
Store in the refrigerator before use.

Mix the pectin X58 with the sugar.
Heat the milk and cream.
At 140°F (60°C), sift in the pectin and sugar mixture and bring to a boil.
Strain the mixture, then grate on the truffle.
Blend it, pour it into a box and place it in the refrigerator.
Tip: if you don’t like truffle, you can replace it with vanilla!

Heat the milk, cream, glucose powder, milk powder and invert sugar.
At 115°F (45°C), add the sugar mixed with the ice cream stabilizer.
At 160°F (70°C), pour the hot mixture onto the Opalys chocolate and stir the two together to create a perfect emulsion.
Pasteurize at 185°F (85°C), sift out any lumps, then grate the truffle into the ice cream mix.
Blend and cool quickly.
Leave to sit for at least 12 hours.
Churn.