Martha's recipe is inspired by a cake that master baker Rose Levy Beranbaum made on the Martha Stewart Show.
Preheat oven to 375 degrees with rack set in lower third of the oven. Brush 12 mini Bundt cake molds with butter and dust with flour; set aside.
In a medium bowl, whisk together flour, baking powder, and salt. Sift flour mixture twice and set aside.
In the bowl of an electric mixer fitted with the whisk attachment, whip cream on low, until soft peaks form. Gradually increase speed to medium-high as cream thickens, and whisk until stiff peaks form, about 3 minutes.
In a medium bowl, whisk together eggs and vanilla. With the mixer on medium-high, gradually add egg mixture; beat until thickened (like mayonnaise) and well combined. Gradually add sugar, about 30 seconds.
Remove the whisk attachment from the mixer. Using the whisk attachment, gently fold half the flour mixture into the cream mixture until flour is dissolved and well combined. Repeat process with remaining flour mixture. Using a large pastry bag, pipe batter into prepared cake molds and run a small metal spatula or dull knife through batter to prevent large air bubbles from forming, avoiding bottom of the pan. Smooth surface evenly with a small metal spatula.
Transfer pans to oven and bake until cakes springs back when lightly pressed with your finger and a cake tester inserted into cakes comes out clean, 18 to 20 minutes. Transfer cake pans to a wire rack and let cool 10 minutes; cakes will begin to shrink from sides of pan.
Spray a wire rack with nonstick cooking spray. Using a metal spatula, loosen top edges of cakes and invert onto prepared wire rack. Let cool completely. Serve with whipped cream and berries, if desired.