For the batter: In the bowl of an electric mixer, beat the butter with the sugar, egg and flour and until well combined. Butter a 10-inch springform pan, scrape the batter into the pan and smooth the top.
For the topping: Rinse the blueberries, drain and pat dry.
Preheat the oven to 180°C (approximately 350°F).
Beat the eggs with the sugar, lemon zest and juice, cream and creme fraiche and pour over the batter. Scatter the blueberries over the top and sprinkle with powdered sugar.
Bake on the lower rack of the oven until a toothpick inserted in the center comes out clean, about 45 minutes. Serve warm or cold. To serve, decorate as desired with blueberry puree.