THE CAKE: Heat the oven to 350°F. Butter a 9-inch cake pan and line the bottom with parchment paper; butter and flour the paper. In a large bowl, mix the butter and brown sugar by hand with a wooden spoon until well combined. Whisk in the eggs and then the buttermilk.
In a separate bowl, sift together the flour, baking soda, baking powder, and salt. Add the flour mixture to the butter mixture, stirring just until the ingredients come together; do not overmix. Stir in the blueberries and the almonds.
Pour the batter into the cake pan. Sprinkle the top of the cake with the remaining tablespoon brown sugar, and sparkling sugar, if desired.
Bake for 55 minutes, or until a wooden toothpick inserted into the center of the cake comes out clean. Let cool completely. Run a thin knife around the edge of the pan and invert cake onto a plate. Flip cake back over onto a cake stand.
THE COMPOTE: Add the strawberries, and simmer 5 minutes or until the strawberries are soft but not mushy. Add the blueberries. Let cool to room temperature. To serve, slice the cake and top each serving with compote and a dollop of creme fraiche.