Preheat oven to 400º. Stack 2 baking sheets together and line the top one with parchment paper.

In the bowl of a food processor, add flour, baking powder, sugar and salt. Process until combined. Add cold butter and process until you have pea size pieces.

In a measuring bowl, whisk together the creme fraiche, vanilla and egg. Add to flour mixture and process just until combined.

Transfer to a floured surface and knead until it just comes together. Pat into a 12 inch square. Cut into thirds and stack on top of each other. Roll it out and repeat two more times. Place in freezer for about 10 minutes. (You can refrigerate this overnight at this point)

Remove from freezer and roll it into a 12 inch square. Add frozen blueberries or fresh, pushing them into the dough. Roll it jelly roll style into a 12 by 4 inch rectangle. Cut the rectangle into 4 equal rectangles and cut each rectangle into 2 triangles. Transfer to baking sheet and brush the tops with heavy cream and sprinkle with coarse sugar.

Bake for 18-25 minutes until tops and bottoms are lightly brown.