Heat the oven to 180C/160C fan/gas 4. Butter and line the bases of two 20cm sandwich tins. Melt the butter in a pan, then remove from the heat and beat in the oil, milk, yogurt, vanilla and eggs. Whisk the dry ingredients together with a large pinch of salt, squishing any lumps of sugar with your fingers. Tip the wet ingredients into the dry, then whisk until smooth.
Divide the batter between the tins and bake for 25-30 mins on the same shelf of the oven until risen and a skewer inserted into the middle comes out clean. Leave to cool for 10 mins in the tins, then transfer to a rack to cool completely.
To make the buttercream, beat together the sugar, butter and a few drops of the red food colouring. Add 2-3 tbsp of boiling water if needed to soften the mixture, until you end up with a smooth, spreadable icing.
Trim the cakes flat if needed, then halve each through the middle using a large serrated knife. Put one cake layer on a board or plate, spread over a thin layer of the buttercream and dot over a third of the jam. Top with another cake layer and repeat with the buttercream, jam and cake, finishing with a layer of cake. Use most of the remaining buttercream to ice the cake all over, reserving a small amount.
Roll the fondant icing out on a surface dusted with icing sugar until large enough to cover the top and sides of the cake. Carefully lift it up onto the cake and smooth down to help it to stick. Use a sharp knife to cut slashes into the icing, then drizzle a little of the reserved buttercream mixed with some water into each to look like blood.