Preheat an oven to 180c (350f) and prepare 3 8-inch baking pans with parchment paper.
Into a big mixing bowl, add the soft butter, and sugar. Mix with an electric hand mixer until creamy and smooth for about 3 minutes.
Into a big mixing bowl, add the buttermilk, vegetable oil, kosher salt, vanilla extract, eggs, sour cream, melted biscoff spread, and mix with a whisk.
Then into a medium mixing bowl, add the flour, baking soda, and baking powder. Mix with a whisk until combined.
Add ½ of the dry mixture and ½ of the wet mixture and the biscoff cookie crumbs into the butter mixer and mix it until almost combined. Add the other half of the dry ingredients and the wet mixture until just combined.
Divide the batter into 3 8-inch baking pans and bake in a 180c (350f) preheated oven for about 25-30 minutes (depends on your oven) or until a toothpick is inserted into the cake comes out clean.
Step 7: Let the cakes cool to room temperature and remove them from the pans.
Make the biscoff buttercream:
Into a big mixing bowl, add the room temperature butter, powder sugar, biscoff spread, vanilla extract, and heavy cream.
Mix with an electric hand mixer for a few minutes until the buttercream is light in color and creamy.
Assemble the cake:
Pipe a small dollop of the biscoff buttercream on the surface that you will frost on. Lay the first cake layer over the frosting dot.
Top the first cake layer with ⅓ of the biscoff buttercream and spread an even layer using a spatula. Top the cake with ⅓ of the biscoff crumbs and spread it on top of the buttercream. Repeat with the second cake layer.
Top the cake with the third cake layer and frost the cake with the remaining buttercream.
Melt the cookie butter in the microwave until it's melted and top the cake with it, use a spatula to carefully push the biscoff butter around the edges of the cake until a drip design forms.
Top the cake with ½ of the biscoff crumbs and biscoff cookies pieces.
Use room temperature ingredients. It is important that you use room-temperature ingredients like eggs and butter. This step ensures that your mixture mixes into a homogenous mixture and bakes perfectly. you don’t want to place cold batter into the oven.Measure your flour correctly! When measuring your flour, avoid scooping it with a measuring cup. Instead, stir the flour with a spoon to create as many air pockets as possible, and spoon it into your measuring cup. Finally, level it with a back of a knife.Don’t overmix the batter, you don’t want to develop the gluten in the flour. This step ensures you have a moist cake and not dense and dry cake.Use cake strips!Cake strips give you even and perfectly baked cake layers. Click here for the amazon link.Line your baking pan with parchment paper! This step helps the cake to bake evenly, and it makes sure that your loaf cake will release easily from the pan.Make sure that your butter is at room temperature. An hour or two before making these cookies, take the butter out of the fridge and let it come to room temperature. The butter should be soft to the touch. If your butter is too cold, it will be harder to mix and there will be lumps of butter in the dough.Be patient! I know it’s extremely tempting to frost this cake as it is pulled out of the oven, but let the cake cool for at least 1 hour so it will be more firm and won’t crumble up, and prevent the frosting from melting.