Preheat the oven to 400 degrees. Coat a muffin pan with cooking spray.
Prepare the muffin batter by whisking together the white sugar, brown sugar and eggs until well creamy and smooth.
Add the buttermilk, oil and vanilla extract then whisk until smooth and creamy.
In a separate dish stir the flour, baking powder and salt together until well combined.
Slowly add half of the flour mixture to the batter and mix. Add the remaining flour and mix until just combined.
Gently fold in nearly all of the raspberries, blueberries and strawberries, leaving a few behind to add to the top later. Pour the batter equally into the muffin pan filling them to the top. Add the remaining few raspberries, blueberries and strawberries to the top of each muffin, as needed.
Sprinkle some coarse turbinado sugar on top of each muffin.
Place into the oven and bake for 5 minutes. Reduce the heat to 350 degrees and continue to cook for 13-15 minutes, or until a tester inserted in the center comes out clean.
Remove from the oven and cool in the pan for a few minutes before putting them on a wire rack to finish cooling. Serve and enjoy. Side Note: Starting the baking at a higher temperature then reducing it helps make the muffin dome.