Preheat the oven to 355 ̊F (180 ̊C) and line your 6 1/2-inch (17 cm) loose-bottom cake pans with parchment paper.
To make the vegan buttermilk alternative, add the apple cider vinegar to the soy milk, stir, and let it thicken for 5 minutes.
In a large mixing bowl, combine the sugar and olive oil and cream together until pale and fluffy.
Stir in the buttermilk and vanilla. Sift in the flour, baking powder, and baking soda. Gently fold these into the wet mixture along with a pinch of salt and mix until smooth.
Place the biscuits into a Ziploc bag and crush them using a rolling pin. Pour these into the cake batter and stir through to evenly distribute.
Transfer the mixture to your cake pans and bake for 30 to 35 minutes. Check to see if your cakes are ready by inserting a toothpick. If it comes out clean, the cakes are cooked through.
Once ready, remove the cakes from the oven and transfer onto a wire rack to cool.
Whip up the frosting by beating the butter until pale and fluffy, which should take 5 minutes. I like to use an electric hand whisk or a stand mixer.
Gradually add the powdered sugar and continue to mix until all the sugar has been incorporated. You can then fold in your creamy Biscoff spread to finish.
To assemble, spread a layer of the frosting onto one of the sponge cakes and make a small well in the center using the back of a spoon. This helps to avoid the filling spilling over the sides of the cake. Fill this with your cookie spread and place the second sponge on top.
Coat the entire cake in the delicious frosting and use a cake scraper and palette knife to achieve a smooth finish. Refrigerate the frosted cake for 5 to 10 minutes (doing so will help avoid your Biscoff drizzle from melting the frosting).
Gently melt the Biscoff spread and drizzle it around the edges of the cake, creating a drip effect. To melt the spread quickly, you can use a microwave, checking at 15-second intervals.
Add the remaining frosting to a piping bag fitted with a star-tip nozzle, and pipe swirls all around the edge of your cake. Garnish with Lotus Biscoff biscuits and serve.