Pre-heat your oven to 160C Fan/350F/Gas Mark 4, and grease and line three 8" cake tins (that are at least 2" deep)
Make the sponge by mixing the butter and light brown sugar in a large bowl until fluffy, ideally using an electric mixer
Add the Biscoff spread and mix in
Add the eggs and milk, and whisk until fully incorporated
Gently whisk in the self raising flour, and whisk in until you can't see any flour anymore
Divide the mixture between the tins, use scales for accuracy if you like
Bake them for 35-40 minutes or until a skewer inserted in the middle comes out clean. Leave them to fully cool either in the tins or remove from the tin and place on cooling racks
To make the buttercream, use an electric mixer or a spoon to mix together the butter and icing sugar until they start to combine, then add the Biscoff spread and milk and mix until smooth. You can add more milk if the buttercream is too stiff
If the cakes have domed on top, level them off with a cake leveller or a serrated knife
To decorate, place one of the cake sponges on a decorating turn table with a cake board underneath it (and a non slip mat underneath the cake board)
Spread or pipe buttercream over the cake, then add the second cake layer, spread more buttercream over that, then add the third and final cake layer on top
Cover the whole cake with a base layer of buttercream (a crumb coat). Put it in the fridge for 30 minutes to firm up
Coat the cake with a second and thicker layer of buttercream and smooth it out as best you can using a buttercream scraper/smoothing tool. Then put it back in the fridge for 30 minutes to set and firm up
Melt the Biscoff for the drip in the microwave for 20 seconds, or until it's a pourable consistency. Put it in a piping bag or a squeezy bottle, or you can use a spoon
Pipe the Biscoff around the edge of the cake, allowing it to drip down the sides in varying amounts
Once the drips are complete, cover the whole top of the cake with the remaning Biscoff spread. Use a palette knife to smooth it out. Put the cake in the fridge for 30 minutes for the Biscoff to firm up
Put the remaining buttercream into a piping bag with your chosen nozzle and pipe swirls all around the edge of the cake
Decorate with Biscoff biscuits, the biscuits will go softer after being in contact with the buttercream so do this as close to serving the cake as you can
Leftovers will keep in an airtight container in a cool place for 3 days