To prepare the rhubarb jam:

1. Combine all of the ingredients in a medium-sized pot over low heat. Stir to combine and continue stirring regularly until all of the sugar has dissolved. You can test this by carefully rubbing a little bit of the liquid in the pot between two fingers- it should feel smooth.
2. Continue to cook over low heat, stirring regularly until the mixture comes to a simmer. Allow it to simmer for about 10-15 minutes until the rhubarb and berries have broken down and the mixture is approximately applesauce consistency. Remove from heat and place in a heat-proof bowl to cool in the fridge. This jam will keep in the fridge for approximately 2-3 weeks.

To prepare the streusel crumbs:

1. Preheat the oven to 350 degrees.
2. In a small saucepan over medium heat melt and brown the butter. See the link in my blog post for help on this. Whisk the flour, brown sugar, oats, salt, cinnamon and ginger together in a medium sized bowl. Add the browned butter to the mixture 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 cake:

1. Preheat the oven to 350 degrees. You can opt to make a 2 layer 8” cake or a 3 layer 6” cake. Whichever you choose, grease your pans and line the bottom of each with parchment rounds.
2. In a large bowl or the bowl of a stand mixer, cream the butter, sugar, and vanilla on medium speed (I use 4 on my mixer) until light and fluffy. Scrape the sides of the bowl and add the eggs one at a time. Beat for an additional minute. Add half of the flour, the baking powder, and salt, and stir on low to combine. Scrape the sides of the bowl and add half of the buttermilk. Repeat this process with the remaining half of the flour and buttermilk. Scrape the sides of the bowl and fold in any unincorporated bits of batter. Divide the batter among the pans and bake in the oven until the top is lightly golden and a toothpick inserted comes out clean. For 3 6” cakes, this will take about 25-27 minutes. Allow the cakes to cool completely before assembling.

To prepare the jam buttercream:

1. In a large bowl or the bowl of a stand mixer, cream the butter at medium speed until light and fluffy, about 2 minutes. Scrape the sides of the bowl and add the powdered sugar, extracts, and salt. Stir to combine and add the ¼ cup of jam. You’ll likely need an additional 2-3 tablespoons of jam to thin the buttercream out to spreading consistency. Beat in the mixer for an additional minute until smooth and combined, and add a tablespoon of milk or water as needed to get the right consistency for spreading.

To assemble your cake:

1. Level the cakes using a serrated knife. Spoon 1/3 of your frosting into a piping bag or large plastic bag with a hole snipped in the end so you can pipe a dam around the border of your cakes. Place a small amount of buttercream on a cake board or serving platter and place your first cake directly on top. Spread a small amount of buttercream on top of that layer and then use your piping bag to pipe a “dam” around the perimeter of the cake. The dam can be narrow but should be about ¼-1/2” tall. Spoon jam inside of the dam just barely under the top of the dam and then sprinkle streusel on top. Stack the next layer of cake and then repeat this process again finishing with the 3^rdlayer of cake. Spread the remaining icing around the outside of the cake and decorate as desired! The cake is best stored covered in the fridge and then brought barely to room temp prior to serving.