To prepare the streusel crumbs

1. Preheat the oven to 350 degrees.
2. Whisk the flour, brown sugar, oats, and salt together in a medium sized bowl. Add the melted butter and fold together until the ingredients clump into dime-sized bits. Spread out on a sheet pan and bake in the preheated oven, tossing occasionally, for 10-12 minutes or until the streusel is golden brown. Allow to cool completely before using or storing. Streusel can be made ahead and stored at room temperature for a week, or in the freezer for a couple of months.

To prepare the raspberry filling

1. Combine all of the ingredients in a small saucepan over medium heat. Stir well to evenly coat the raspberries. As the raspberries cook, smash with the back of a fork or with a potato masher. Once the mixture is smooth, bring to a boil, stirring regularly, until the mixture has thickened slightly. Remove from heat to a small bowl and cover the top with plastic wrap. Chill completely in the refrigerator completely prior to using.

To prepare the cake

1. Preheat the oven to 350 degrees. Grease the sides and line the bottoms of 3-8” round cake pans with parchment paper and set aside.
2. In a small bowl, combine the cake flour, baking powder, and salt and set aside.
3. In a large bowl or the bowl of a stand mixer, cream together the butter, sugar, and brown sugar on medium speed until light and fluffy, about 2 minutes. Scrape the sides of the bowl with a spatula and add each egg one at a time on low speed, mixing just until combined. Scrape the sides of the bowl. Add about 1/3 of the dry ingredients followed by the vanilla and about half of the buttermilk. Mix until combined and then repeat this process once more, finishing by adding the last third of the dry ingredients. Scrape the sides of the bowl and fold in any unincorporated bits of batter.
4. Distribute the batter evenly among the three pans and bake in the preheated oven 20-25 minutes or until a toothpick inserted comes out clean. Allow to cool completely prior to assembling cake.

To prepare the frosting

1. In a large bowl or the bowl of a stand mixer, beat the butter on medium speed (I use 4 on my stand mixer) for 2-3 minutes until light and creamy, scraping the bowl as necessary. Add the cream cheese and beat to incorporate for an additional minute. Add the salt, vanilla, and powdered sugar and beat on low speed until incorporated. Scrape the sides of the bowl and continue to beat until well combined. Do not overbeat as this can cause the cream cheese to loosen. If needed, add a tablespoon of water or milk at a time to get the frosting the right consistency. Refrigerate as needed to thicken the frosting up.

To assemble the cake

1. Use a serrated knife to level the cakes. Smooth a small amount of frosting on an 8” cake board or plate and center a single cake layer on top. Using a piping bag (see notes) fitted with a large round tip, pipe a dam around the outer rim of the top of the cake. The dam should be at least ¼” tall to prevent the raspberry filling from squirting out the sides. Spread approximately half of the raspberry filling inside the dam and sprinkle with about 1/3 of the streusel crumbs. Pipe a bit of frosting on top of the raspberry filling to help the next layer of cake stick. Stack the second cake layer on top and repeat the entire process once more. Place the final cake layer on top. Spread a thin coat of frosting (crumb coat) all over the cake and allow it to set up in the fridge prior to applying the final coat of frosting. You can skip this step if desired. Decorate the top of the cake with a few streusel crumbs and spare raspberries, if desired. Cake will keep in the refrigerator covered in plastic for up to three days.