Line the base of a loose-bottomed 25 x 35cm cake tin and brush the sides lightly with oil. 

To make the base, place the biscuits in a zip-lock bag and crush to a fine crumb with a rolling pin. Add the biscuits to a bowl and stir in the melted butter. Mix well.

Tip the mixture into the tin and press into an even layer using the back of a spoon. Allow the base to chill in the fridge while you make the marshmallow.

To make the marshmallow, place the egg whites in a mixer and whisk until soft peaks form. Put the Dr. Oetker Platinum Grade Gelatine Leaves in a deep bowl or jug, cover fully with cold water and set aside to soften.

Put the caster sugar, honey and 300ml water in a large pot and stir to combine well. Cook over a medium-high heat until the mixture reaches 130 ̊C on a thermometer. Remove from the heat

Squeeze the water out of the gelatine and add to the hot sugar; you may want to wear oven gloves as the sugar can bubble up and spit. Stir until the gelatine has dissolved, then carefully pour the mixture into a heatproof jug. 

Turn on the mixer with the egg whites and whip further until stiff peaks form. Keep whisking while you slowly pour in the hot syrup in a steady stream. Keep beating the mixture until smooth and shiny, then add the vanilla seeds. Continue to beat for 5-7 minutes or until the mixture is thicker and somewhat cooler

Pour in the marshmallow mixture onto the biscuit base and smooth the top with a spatula. Leave the marshmallow to set for two hours

To prepare the ganache, place the Dr. Oetker Dark Chocolate Chunks in a heat-proof mixing bowl. 

Heat the cream in a saucepan over a medium heat, stirring constantly. When bubbles have formed at the edges of the pan, remove it from the heat and pour the cream over the chocolate.

Add the salt and leave the chocolate to stand for five minutes, without stirring, until it looks soft.

Whisk the chocolate until smooth and shiny, then pour over the marshmallow and leave to set for one hour. Slice into 25 even squares or rectangles and serve.