Preheat oven to 350 degrees. Spray three 6" cake pans with cooking spray and line with parchment paper.
In a large bowl combine flour, baking powder and salt. Set aside.
Using a stand mixer fitted with a paddle attachment, beat the butter on high until creamed (about 1 minute). Scrape down the bowl as needed.
Add both sugars and beat until creamed (about 2 minutes).
Add the eggs and vanilla and beat on medium until combined. Scrape down the bowl.
Slowly add the dry ingredients while beating on low speed.
Add the buttermilk, orange zest and orange juice. Mix on the lowest speed to fully combine, but don't overmix.
In a small bowl, toss the raspberries with the one tablespoon of flour (this will prevent the raspberries from sinking to the bottom). Fold the raspberries into the batter.
Divide batter between prepared cake pans. Bake for 30-40 minutes or until a toothpick inserted in the center comes out clean. (It took our 6 inch cakes about 35 minutes)