Preheat oven to 350.

Grease the bottom of 2 9 inch cake pans and line with parchment paper.

In a medium bowl, sift together the flour, baking soda, baking powder, and salt.

Beat the butter with the sugar until light, 1 min on medium-high speed with a stand mixer or 3 min handheld.

On medium speed add the eggs, one at a time, beating for 30 seconds and periodically scraping the bowl.

Stir together the buttermilk, and vanilla.

On low speed add half the buttermilk.

Mix until incorporated and scrape down the bowl.

Add half the dry ingredients and mix again.

Repeat with last half of buttermilk and dry ingredients.

Fold in the poppy seeds.

Divide the batter between two pans.

Bake on the middle rack until a skewer inserted in the middle comes out clean, 15-20 min (Mine always take a little longer, but make sure to watch!)

Cool the cakes in their pans for 10 min and remove.

Once the cakes are completely cool use a serrated knife to cut each in half horizontally, making 4 layers.

In a plastic container, stir together cream and buttermilk.

Cover with an airtight lid and store at room temperature for 24 hours.

Stir and cover.

Again let sit for 24 hours.

If the cream fraiche is thick, refrigerate. If it is still thin, let sit another 24 hours.

Cook the blueberries in a saucepan over medium-low heat with 1/4 cup sugar.

Stir often until the berries are beginning to pop and the juices are flowing.

Let cool to room temp.

Whip together the creme fraiche, 2 Tablespoons sugar, and heavy cream until stiff enough to hold its form.

Place a cake layer on a serving platter.

Spread one quarter of the creme fraiche filling on the cake and top with 1/4 the berries.

Repeat layers.