Brush 4 ramekins with vegetable oil and wipe off any excess with kitchen paper; put the gelatine leaves in a small dish, cover them with cold water and leave them to soak for 5 minutes until softened
In a small bowl, whisk 2 tablespoons of the milk with the cocoa powder and set it aside; pour the remaining milk and the double cream into a saucepan, add the chocolate, honey and vanilla seeds and heat until the chocolate and honey have melted
Remove the pan from the heat; pour some of the heated mixture over the cocoa and milk mixture, then pour it all back into the saucepan and whisk to mix thoroughly; wring out the excess water from the gelatine sheets and add them to the saucepan; put the pan over a gentle heat and stir until the gelatine has dissolved; don’t let the mixture boil
Pour the mixture through a sieve into a jug, then divide it between the ramekins; cover the panna cottas with clingfilm and leave them to cool, then put them in the fridge overnight
Before serving, dip the ramekins into hot water for a few seconds to loosen; turn out on to serving plates and serve with chocolate shavings
4 servings