Start by preheating your oven to 325°F then liberally spray 3 (8-inch) round cake pans with non-stick baking spray or grease and flour.
In your mixer bowl, add oil and butter and beat for 2 minutes on high speed. Slowly add in sugar and beat on high speed for an additional 4-5 minutes until very pale yellow and fluffy. Next, add eggs, one at a time, combining well after each addition and scraping down the sides as needed.
Turn your mixer down to its lowest speed, and slowly add flour into batter in two increments then add baking powder, salt and baking soda. Be careful not to over beat.
Lastly, add sour cream, milk, and vanilla extract, scrape down sides and mix until just combined and turn off mixer.
Evenly pour cake batter into prepared baking pans and place in oven to bake for 17-27 minutes or until a toothpick inserted into the center of the cake comes just barely clean but don't over bake!! I personally start checking the cakes around 16 minutes just to be sure since everyone's oven is different.
Remove cakes from oven and rest in pans for 10-15 minutes. Invert cakes from pans onto cooling racks until cooled.
For the Berries
Stir strawberry slices with sugar and vanilla to combine in a medium sized bowl. Cover and set aside.
For the Buttercream
Put an inch of water in a medium saucepan and bring to a gentle boil. In the bowl of your stand mixer, stir egg whites, sugar and salt until combined.
Place mixing bowl over saucepan but be careful not to let the water touch the bottom of the mixing bowl.
Stir with a spatula until the sugar dissolves and reaches a temp of 160 F, about 5 minutes. While you stir, scrap the sides of the bowl to ensure no sugar grains are lurking on the sides.
Remove mixing bowl from heat and add to stand mixer with whisk attachment. Whisk on medium high speed until stiff peaks form. They will be glossy. This can take up to 10 minutes. The bowl will continue to cool down in the process as well.
Reduce the speed to low and add 1 to 2 tablespoons of butter at a time making sure to mix in thoroughly after each addition. When butter is incorporated, add vanilla extract, strawberry jam and if desired, food coloring to reach a soft pink color, and beat on low until incorporated then frost or refrigerate until ready to frost.
To assemble the cake, use a cake leveler or serrated knife to cut the domes off the top of the cake if desired. Place a dollop of buttercream on your cake board and place the bottom layer of cake on top of that.
Place half of the swiss meringue buttercream in a large piping bag fitted with a large open round tip or with the end cut off. Pipe a thick dam of buttercream along the outside edge of your cake.
Add half of the strawberries to the layer inside of the dam of buttercream. The dam will make sure the berries stay inside.
Pipe another layer of buttercream over the mascerated strawberries and spread evenly with your offset spatula.
Next add your second layer of cake and repeat all steps (creating the dam, adding the berries inside and spreading the buttercream on top).
Finally add the final layer of cake and frost with the remaining buttercream starting with a crumb coat then allow it to set in the refrigerator for 30 minutes before completing your frosting job. Store your cake in the refrigerator and allow slices to come to room temperature for serving.
Because this cake has berries, it can spoil quickly. It should be stored in the refrigerator and after 1-2 days, freeze the remaining slices and bring to room temperature when you want to enjoy.