If you have fresh berries on hand you are in for a real treat if you make this cake. It's perfect for a party as it is not a cake that keeps well and probably should be eaten on the same day it is made, but wow, it is delicious!
Grease the bottom and sides of two 9 inch cake pans.
Line the bottoms with parchment paper.
In a medium bowl, sift together the flour, soda,salt and baking powder.
Beat the butter with the sugar until light.
Add the eggs, one at a time, beating well after each addition.
Stir together the buttermilk and the vanilla.
On low speed, add half the buttermilk and mix until incorporated well.
Add half the dry ingredients.
Mix well and then repeat until all dry and wet ingredients are mixed in well.
Stir in the poppy seeds.
Divide the cake batter between the two pans.
Evenly spread it in pans and bake on the middle rack of the oven until a skewer comes out clean, about 15 to 20 minutes.
Cool the cakes in their pans for 10 minutes, then turn out and cool completely.
The cake layers can be made up to 2 days in advance; wrap well and store at room temperature.
To make the filling; cook the blueberries and 1/4 cup sugar in a small saucepan over medium-low heat, stirring often, until the sugar has dissolved and the berries have popped open and become juicey, about 5 minutes.
Let cool to room temperature.
Whip together the creme fraich, cream and remaining 2 TBS sugar until stiff enough to hold it's shape but is still smooth.
To assemble the cake, cut the cake layers in half horizontally using a serrated knife, making a total of 4 layers.
Place a cake layer on a serving plate.
Spread one quarter of the creme fraich filling on top of the cake.
Top with one quarter of the blueberry sauce and then one quarter of the raspberries.
Place a second cake layer on top and spread creme fraich, blueberry sauce, and raspberries on top as you did with the first layer.
Repeat with the third and fourth layers, ending with berries on the top of the cake.
If not serving within an hour, refrigerate the cake.
Once removed from the refrigerator, let sit at room temperature for 15 minutes before serving for optimal flavour.