In a stand mixer fitted with the whisk attachment, combine the egg whites, salt, and cream of tartar. Start the mixer on low, then increase the speed to high, whipping until stiff peaks form.
When the egg whites are stiff, with the machine running on high, gradually add ½ cup maple syrup, 1 tablespoon at a time.
Once the maple syrup has been incorporated, fold in the tapioca starch, ¼ cup at a time.
Put the mixture into an ungreased 9-inch springform pan and run a knife through the batter to break up any air pockets. Bake for 30 minutes or until golden brown and set. Place the pan on a wire rack to cool for at least 1 hour – the cake will sink a bit in the middle, this is OK. Run a knife around the edges of the pan, release the outer ring, and remove the cake from the pan. Cut the cake in half horizontally.
Whip the cream with 2 tablespoons maple syrup until soft peaks form.
Place one half of the cake on a serving platter or cake stand. Spread with a thin layer of jam, then about ¼ of the maple whipped cream.
Spread a thin layer of jam on the remaining cake half and place, jam side down, on top of the cream. Frost the cake with the rest of the maple whipped cream. Top with berries.
Refrigerate until serving time – best to refrigerate for at least 1 hour before serving.