Preheat your oven to 350 degrees F and spray 4 6-inch cake pans heavily with a nonstick spray. Sprinkle them with flour and set aside.
In a large bowl, whisk together the flour, baking powder, baking soda, and salt. Set aside.
In the bowl of your stand mixer, with paddle attachment fixed, cream the butter and sugar together. Beat for about 2 minutes. Mix in the vanilla extract, and then beat in each egg, one at a time. With the mixer set on low speed, mix in 1/2 cup of the buttermilk. Next add 1/3 of the flour mixture, and then mix in the remaining buttermilk. Add an additional 1/3 of the flour mixture, 1 cup of milk, and then the remaining 1/3 of flour mixture. Remove the bowl from the mixer and fold the ingredients together if you still have traces of flour. Divide the batter equally among the 4 cake pans.
Bake the cakes for 30 minutes or until brown on top and a toothpick comes out clean. Let them cool completely in the pan.
While your cakes are cooling, prepare your cannoli cream filling and vanilla buttercream. For the cannoli cream, add the heavy cream to the bowl of your stand mixer with whisk attachment fixed. Beat until soft peaks form. Set aside. Also to the bowl of your stand mixer, with whisk attachment fixed, add the ricotta cheese, cream cheese, powdered sugar, and ground cinnamon. Beat on medium speed for about 1 minute. Remove the bowl from the mixer and then fold in the whipped cream. Place in the refrigerator until you are ready to use.
In the bowl of your stand mixer, with paddle attachment fixed, beat the powdered sugar, salt, butter, and vanilla extract until smooth. Add milk, 1 tablespoon at a time, until it reaches the consistency you desire. It should be intact but still spreadable. Set aside.
To assemble your cake, place one cake layer on work surface. Pipe buttercream along the inside edge to create a small well. Place about 1/3 cup of cannoli cream in the center and spread it around, meeting the edge of the buttercream well. Top the cannoli cream with a couple tablespoons of buttercream and spread. Place the second cake layer on top, and repeat with the buttercream well and cannoli cream. Do this a third time. When you reach the fourth cake layer, you are finished with the cannoli cream. Refrigerate any extra for use later on. Using your remaining buttercream, dollop a couple of tablespoons on top. Spread it out evenly. Also dollop buttercream along the creases of the cakes, and spread out evenly. Enjoy!