Melt the chocolate in a thin-sided bowl over a gently simmering bain-marie, ensuring that the bowl does not touch the water.
Mix the flour, baking soda, cocoa, icing sugar and vanilla in a large bowl. Add the oat milk, maple syrup, oil and melted chocolate, mix into a thick batter, stir in the vinegar at the end. Transfer the batter to the prepared tin.
Approx. 35 mins. in the centre of an oven preheated to 170°C. Test with a skewer. Remove from the oven, allow to cool slightly, remove from the tin, turn out onto a rack and leave to cool. Using a knife, cut the cake horizontally into 3 equal pieces.
Thoroughly mix all of the ingredients. Spread 2 of the cake bases with 1/3 of the ganache each, precisely lay both bases on top of each other, place the 3rd base on top (baked side up), press down gently. Cover the remaining third of the ganache and set aside.
Heat the oat milk and icing sugar in a small pan, stirring until the sugar has dissolved. Add the chocolate, melt over a low heat while stirring. Allow to cool slightly, stir in the peanut butter. Cover the glaze and chill for approx. 1 hr.
Spread the glaze over the cake, smooth down. Transfer the reserved ganache to a piping bag, use to decorate the cake.