Make the cake:
1. In a medium bowl, whisk together the flour, baking powder, baking soda, and salt.
2. In a large bowl, cream together the butter and sugar until light and fluffy.
3. Beat in the egg yolks one at a time, then stir in the vanilla extract and orange zest.
4. Alternately add the dry ingredients and buttermilk to the butter mixture, beginning and ending with the dry ingredients. Mix until just combined.
5. Divide the batter evenly between three greased and floured 8-inch round cake pans.
6. Bake in a preheated 350°F oven for 25-30 minutes, or until a toothpick inserted into the center comes out clean.
7. Let the cakes cool in the pans for 10 minutes before transferring them to wire racks to cool completely.

Make the lime frosting:
1. In a large bowl, cream the butter and powdered sugar until light and fluffy.
2. Beat in the lime juice and vanilla extract until smooth.

Assemble the cake:
1. Place one cake layer on a serving plate and spread with a layer of lime frosting.
2. Top with a layer of mixed berries.
3. Repeat with the remaining cake layers, frosting, and berries.
4. Decorate the top of the cake with additional berries and lime slices.