• Heat the oven to 350 degrees F. Grease an 8-inch spring form pan and place on a baking sheet.
• Arrange the plums in single layer in the bottom of the spring form pan. Sprinkle the plums with brown sugar.
• Melt the 2 tablespoons of butter over medium heat until just browned. Butter will melt, foam and froth, then begin to brown along the bottom. Whisk the browned bits of butter off the bottom of the pan. Pour the butter over the plums and place the plums in the oven for 10 minutes.
• Meanwhile, add the whole wheat flour, white flour, baking powder, vanilla and sea salt to a bowl, set aside.
• To the bowl of a stand mixer or large mixing bowl, beat the butter until fluffy. Slowly add the maple syrup, 1 tablespoon at a time, until it is fully mixed into the butter. Beat in the lemon zest, 3 egg yolks (reserving the whites for later) and the yogurt and milk until creamy and smooth, about 1-2 minutes.
• Add the dry ingredients to the wet and mix until just combined.
• Whisk the remaining 3 egg whites in a separate bowl with an electric mixer until soft peaks form. Slowly fold the egg whites into the batter until just combined.
• Pour the batter over the plums, being careful to spread the batter in an even layer over the plums. Try to not move the position of the plums.
• Bake for about 50-60 minutes, or until golden on the top and baked all the way through. Remove from oven and let cool 5 minutes before removing the sides. Place a serving plate on top of the cake and invert the cake. Carefully remove the bottom of the spring form pan. if any of the plums stick to the spring form pan, just place them back on the cake. Scrape any syrup left on the bottom of the pan off and onto the cake. If desired, the cake can be drizzled with a little maple syrup for extra sweetness.
• To serve, sprinkle the cake with pistachios and dollop with cream (recipe below). Enjoy warm or at room temp.

Whipped Yogurt

• Place the cream and yogurt in the bowl of a stand mixer and whip until soft peaks form. Stir in the hazelnut liquor, vanilla and salt. Keep cold until ready to serve.