Position your oven rack into the middle of the oven and preheat oven to 350 degrees Fahrenheit. Spray a 13"x9" baking dish with non stick cooking spray and set aside.
In a large bowl, beat softened butter, strawberry jello, and sugar until fluffy, about 2-3 minutes. Add eggs and vanilla extract and mix well.
In a separate small bowl, add flour, baking powder, baking soda, and salt and whisk to combine.
To the large bowl with jello and egg mixture, add half of the flour and mix well. Add all of the buttermilk (or soured milk) and mix well. Lastly, add the rest of the flour and combine.
In a food processor or blender, add about 8-10 strawberries and blend for 1 minute. This should make about 3/4 cup of puree.
Add in 1/2 cup of strawberry puree and mix well until puree is thoroughly combined.
Pour the cake batter into the prepared baking dish and place in the oven and bake for 35-40 minutes. Check your cake with a toothpick after 35 minutes. If toothpick comes out clean, pull from oven, and allow the cake to cool completely.