Prepare the cakes. Preheat the oven to 350 degrees F. Spray three, 8-inch cake pans lightly with gluten-free cooking spray. Line each of the bottoms with a round of parchment (use a pan as your guide to cut rounds of parchment) and spray again. Set aside.
Mix the flour, baking powder, baking soda, and sea salt in a large bowl and set aside.
In the bowl of a stand mixer fitted with the paddle attachment, beat the butter until smooth. Add the sugar and beat for a couple of minutes until light and fluffy. Add the eggs one at a time and beat until combined. Repeat with the egg whites. Stir in the vanilla.
Add half the flour mixture to the butter and beat to combine. Add the milk and sour cream and the remaining flour mixture and beat until smooth. Pour the batter evenly between the three prepared pans and smooth with an offset spatula so they are even.
Bake on the center rack of the oven for 30 minutes, or until a toothpick inserted in the center of the cake comes out clean. Cool in the pans for 10 minutes, then run a knife around the edges of the pan and invert onto a cooling rack. Cool cakes completely. At this point, I usually wrap the cakes in plastic and freeze over night so they are easier to work with.
Make the strawberry syrup. Put strawberries, sugar and vanilla in a small sauce pan and heat over medium heat, stirring constantly. Cook for about 10 minutes, or until the strawberries give off their juice and it begins to thicken. Remove the cooked strawberries with a slotted spoon and set aside, reserving both the syrup and the strawberries. Cool both completely (the freezer can help speed this process).
Make the whipped cream. In the bowl of a stand mixer fitted with a whisk attachment add the cream. Beat until soft peaks form. Add the powdered sugar and vanilla extract and beat again until firm peaks form. Refrigerate until ready to use.
Make the buttercream. In the bowl of a stand mixer fitted with a paddle attachment beat the butter until fluffy. Add the powdered sugar and about half the milk. Beat until it begins to come together, adding more milk as necessary to get it to a spreadable consistency.
Now it's time to assemble the cake. Stem and slice about half a pint of strawberries, and set aside. Spread a thin layer of buttercream over whatever cake base you are using to help the cake stay put.
Place one layer of the cake on the base. Spread the top thinly with buttercream leaving about a ½ inch border around the edge of the cake.
Snip the bottom off of a piping bag and fit it with the star tip. Fold down the edge of the bag and fill it with about ¾ of the prepared buttercream frosting. Pipe a rim of frosting stars around the edge of the cake using your star tip.
Put a large dollop of whipped cream into the middle of the round and spread to the inner edges of the frosting stars. Set fresh strawberry slices around the edge of the cake over the frosting stars, pointy ends going out. Spoon ½ of the cooked cooled strawberries over the whipped cream. Top with the second layer of cake and repeat the process.
Top with the third layer of cake and repeat the process up to the point where you set fresh strawberry slices around the edge of the cake. Then top the cake with stemmed, whole and sliced strawberries (in a pile or decoratively) using additional whipped cream to hold them in place if necessary. Pipe buttercream stars around the base of the cake.
Drizzle the top of the cake with reserved, cooled strawberry syrup, and garnish with mint or even fresh flowers if you want. Keep refrigerated until you are ready to serve it.