Preheat the oven to 350°F. Grease two 8-inch round cake pans and line the bottoms with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda, cinnamon and salt. Set aside.
In a large bowl, whisk the buttermilk, yogurt, brown sugar and granulated sugar until the sugar mostly dissolves. Whisk in the oil, melted cookie butter and vanilla until smooth and glossy.
Add the dry ingredients to the wet mixture in two additions, folding gently with a spatula just until no dry streaks remain.Do not overmix, as this keeps the crumb soft and tender. Divide the batter evenly between the prepared pans and smooth the tops.
Bake for 28-32 minutes, until the tops spring back when lightly pressed and a toothpick inserted in the center comes out clean. Cool in the pans for 10 minutes, then turn out onto a wire rack and cool completely.
For the frosting, beat the butter and cookie butter with a mixer for 2 minutes until creamy. Add the powdered sugar and salt, beat on low until combined, then add the heavy cream one tablespoon at a time and beat on high for 2 minutes until light and fluffy.
Place one cake layer on a serving plate, spread with a generous layer of frosting and top with the second layer. Cover the top and sides with the remaining frosting and smooth with an offset spatula.Warm the cookie butter for the topping until pourable and drizzle it over the top, letting it drip down the sides. Crush 4 Biscoff cookies over the top and tuck the remaining cookies into the frosting around the edge.