The fresh strawberry puree is simply a cup of blended strawberries. Measure the puree after the strawberries are blended and it should equal 1 cup.
Preheat the oven to 325ºF. Grease and flour two 9" round cake pans (*see instructions below for 9x13 cake pan*).
In the bowl of a stand mixer, combine the cake mix, gelatin, milk, oil, eggs and fresh strawberry puree.
Beat on low speed until mixed, then beat on medium speed for 2 minutes, scraping the sides of the bowl as needed.
Divide the cake batter evenly between the two prepared pans.
Bake for 29 minutes, or until the top of the cake bounces back when you touch it.
Allow the cakes to cool for 10 minutes, then turn them out onto a wire rack to cool completely.
For the Frosting:
In the bowl of a stand mixer, cream the room temperature butter for 1-2 minutes until nearly white in appearance.
Add 2 cups of powdered sugar and the vanilla extract. Beat on low for 1 minute. Scrape down the sides of the bowl.
Mix in the heavy cream* and another 2 cups of powdered sugar. Beat on low for 1 minute. Scrape down the sides of the bowl.
Add the last 2 cups of powdered sugar and the strawberry jam. Beat on low speed until mixed, then beat on medium speed for 1-2 minutes, until the frosting is creamy and smooth, scraping down the sides as needed.
To Frost the Cake:
Place one cake layer on a cake plate.
Spread frosting on top of the first layer. (Add a layer of strawberry jam here, too, if you'd like!)
Place the second cake layer on top of the frosting.
Use the remaining frosting to frost the top and sides of the layer cake.
Optional: Decorate the top middle of the cake with a few tablespoons of strawberry jam and fresh strawberries.
Store in an airtight container in the fridge until serving.
*Add additional heavy cream by the tablespoon until it is to the consistency you'd like.
**To make a 9x13 cake, prepare the cake as described above. Pour the cake batter in a greased 9x13 cake pan. Bake at 325 degrees for 35 minutes, or until the center of the cake bounces back when you touch it.
***If you make a 9x13 cake, you won't need quite as much frosting. Use these amounts for frosting, preparing it in the same way as described above:
1 cup butter, softened
4 cups powdered sugar
1 teaspoon vanilla extract
4-5 tablespoons heavy cream
1/3 cup strawberry jam
If all you have is unsalted butter, use that and add a dash of salt.
Refer to the article above for more tips and tricks.The calories shown are based on the cake being cut into 15 pieces, with 1 serving being 1 slice of cake. Since different brands of ingredients have different nutritional information, the calories shown are just an estimate. **We are not dietitians and recommend you seek a nutritionist for exact nutritional information. The information in the nutrition box are calculated through a program and there is room for error. If you need an accurate count, I recommend running the ingredients through your favorite nutrition calculator.**