For the cake: Preheat the oven to 350 degrees F. Grease and line the bottoms of two 8-inch cake pans with nonstick cooking spray and set aside.
In a large bowl, whisk together the flour, granulated sugar, cocoa powder, baking powder, baking soda and salt. In a separate medium bowl, whisk together the milk, tahini, oil, vanilla and eggs. Add the wet ingredients to the dry ingredients and stir to combine. Whisk in the coffee.
Pour the batter into the prepared cake pans and bake until a toothpick inserted into the center comes out clean, about 28 minutes. Let cool in the pans on a rack for 10 minutes and then remove to the rack to cool completely.
For the frosting: In the bowl of a stand mixer fitted with a paddle attachment, mix together the butter and tahini until creamy. Gradually add the confectioners' sugar and mix to combine. Mix in the vanilla, cinnamon and salt.
Put one cake layer on a serving plate and top with some of the frosting, then top with the second cake layer. Frost the top and sides of the cake and serve at room temperature.