Butter and sugar ramekins and place 5 or 6 berries in each one. With a whisk attachment, whip the yolks with 1/2 cup sugar until light and fluffy. Mix in the vanilla, melted butter, lemon zest, and buttermilk.
Stir the dry ingredients together and slowly mix them into the yolks.
In a separate bowl, whip the whites until stiff then fold them into the batter.
Pour the batter into the prepared molds filling almost to the top. Place them in a water bath and cover with foil. Bake for 30 minutes. Remove from the oven and let set 5 minutes before turning the cakes out of their molds.
To serve, mash the remaining raspberries with the 1 to 2 tablespoons of sugar to make a rough pureed mash. Stir 2 tablespoons sugar into the yogurt. Place the cake on a plate and ring it with the sweetened yogurt and drizzle some raspberry mash through the yogurt.