Preheat the oven to 350°F (180°C). Spray two 8-inch cake pans with non-stick spray and line the bottoms with circles of parchment paper.
Sift all purpose flour into a mixing bowl and add white granulated sugar, baking soda and salt. Mix together.
Prepare your vegan buttermilk by adding 1 ½ tablespoons of lemon juice to a measuring jug and then adding soy milk up to the 1 ½ cup (360ml) line. Let it curdle into buttermilk.
Add the vegan buttermilk, melted biscoff cookie butter, canola oil and vanilla extract and mix it into a batter. Don't overmix.
Divide the batter evenly between the two prepared 8-inch cake pans.
Bake for 30 minutes or until a toothpick inserted into the center of one of the cakes comes out clean.
Let the cakes cool in the cake pans for a few minutes and then transfer them to a wire cooling rack to cool completely.
Prepare your frosting. Add vegan butter and biscoff cookie butter to the bowl of your stand mixer and beat them together until smooth and creamy.
Add powdered sugar and 1 Tablespoon soy milk and beat in until you have a smooth and creamy frosting. If it's too thick, add more soy milk as needed until you have a spreadable consistency.
When the cakes have cooled completely, generously frost the middle, top and sides with frosting.
Decorate the top with melted biscoff cookie butter and a sprinkle of crushed biscoff cookies.
Put the frosted, decorated cake into the fridge for an hour to set before slicing and serving.