1. Begin by making the raspberry rhubarb jam so it has time to cool completely. *note, you only need half of the linked recipe for this cake, the amount is updated in the ingredients list.
   1/2 cup (60g) raspberries whole, 1 cup (120g) rhubarb about 3 stalks, chopped, 3/4 cup (150g) granulated sugar, 1 Tbsp (15mL) lemon juice, 1/2 tsp vanilla extract, Pinch of salt
2. Make one 6 inch vanilla cake and allow it to cool completely to room temperature.
   2 1/4 (270g) cups all-purpose flour spooned and leveled, 1 Tbsp (10g) baking powder, 1/2 tsp salt, 1/4 cup (60g) unsalted butter room temperature, 1/2 cup (120mL) canola oil, 1 1/2 cup (300g) granulated sugar, 3 large eggs room temperature, 3/4 cup (170g) sour cream room temperature, 1 Tbsp vanilla extract, 3/4 cup (180mL) milk room temperature
3. While the cakes are cooling, place the egg whites and granulated sugar in a large bowl. Bring a small pot with 1/2 cup of water to a boil and lower the heat to simmer. Place the bowl of egg whites and sugar on top of the simmering water for 5-10 minutes, until the granulated sugar is completely dissolved, whisking intermittently.
   4 large egg whites room temperature, 1 cup (200g) granulated sugar
4. Once the sugar is dissolved, remove the bowl of egg whites from the heat and use an electric mixer with a whisk attachment to beat the egg whites with the sugar. Beat for 7-10 minutes on high speed and then lower the speed to low-medium.
5. Slowly add 2 Tbsp of butter in at a time. Wait for the butter to incorporate before adding the next chunk. Once all the butter is added, turn the mixer up to high speed for 10-15 seconds, then use a rubber spatula to scrape the edge of the bowl. Add the vanilla bean paste (or extract) and the rhubarb jam to the buttercream, and beat until they're fully combined.
   1 cup (225g) unsalted butter room temperature, 1 tsp vanilla bean paste or vanilla extract, 1/2 cup (175g) raspberry rhubarb jam

Optional

1. Switch the paddle attachment and on low speed, allow the paddle to remove all the excess air from the buttercream (this removes all the air bubbles to ensure a smooth finish when frosting the cake).

Assemble

1. Place the first layer of cake on a cake board or stand. Top with a thin layer of raspberry rhubarb jam and a generous layer of Swiss meringue buttercream. Repeat with the second layer and then place the third layer on top.
2. Smooth out any buttercream that squeezes out between the layers and then refrigerate the cake for at least 30 minutes. Place the rest of the buttercream on top of the cake and use an offset spatula to .work its way down, smoothing out the top and sides of the cake.