Preheat oven to 350°F (175°C). Grease and flour two 9-inch round cake pans.
In a medium bowl, whisk together strawberry puree and buttermilk. Set aside.
In a large bowl, cream together butter, oil, and sugar until light and fluffy. Mix in eggs, one at a time, then add vanilla extract.
In another bowl, sift together flour, baking powder, baking soda, and salt.
Add the dry ingredients to the butter mixture in three additions, alternating with the strawberry-buttermilk mixture. Begin and end with dry ingredients.
If using, mix in food coloring for a vibrant pink color. Fold in diced strawberries.
Divide the batter evenly between the prepared pans. Bake for 25-28 minutes or until a toothpick comes out clean.
Let cakes cool in the pans for 10 minutes, then turn out onto a wire rack to cool completely.