Grate the dark chocolate finely, or chop it in small pieces.
Melt separately the milk and dark chocolate in 2 separate bowls in the microwave for 30 seconds. Stir well to melt the chocolates (if needed put them back for 20 seconds. Then 10 until the chocolates melt well). The chocolate should melt but not exceed 43˚C. (Check with RAY-DIGITAL).
Stir continuously to cool down the 2 chocolates, until they reach 34˚C each.
In a plastic bowl, pour the hazelnut praline.
Pour on top of it the melted milk chocolate first, and then add the dark.
Mix the 3 components well until completely incorporated.
Add the grapeseed oil and stir well.
Pour the mixture in a jar (that has a lid) and put it to set in the fridge uncovered.
When set, take it out from the fridge, cover the jar. Keep it in a dry room temperature place.