Heat oven to 350°F. Spray a 9 x 13 pan with cooking spray.
In a large bowl, cream the butter and sugars together until smooth. Beat in the eggs one at a time. Beat in vanilla.
Place flour, salt, baking soda and powder in a bowl and whisk to combine. Beat in 1/3 of the flour mixture, then 1/2 the sour cream. Beat in half of the remaining flour, then the remaining sour cream, and then the rest of the flour. Beat until batter is smooth.
Gently fold in the strawberries and rhubarb. Spread evenly in prepared pan. Sprinkle with a few tablespoons turbinado sugar, if desired, and bake for 45 minutes, or until cake is lightly browned and a cake tester or toothpick inserted in the center comes out clean.