Preheat oven to 350°F.
Sift powdered Swerve and flour together into a medium bowl. Set aside.
In a large bowl, beat egg whites, cream of tartar, and vanilla with an electric mixer on medium high speed until soft peaks form (tips curl). Gradually add granulated sugar, about 2 tablespoons at a time, beating until stiff peaks form (tips stand straight).
Sift about ¼ of the flour mixture over beaten egg whites; fold in gently. Repeat, folding remaining flour mixture by fourths.
Pour into an ungreased 10-inch tube pan. Bake on the lowest rack of preheated oven for 40-45 minutes or until top springs back when lightly touched. Immediately invert cake (leave in pan); cool thoroughly. Loosen sides of cake from pan; remove cake. Cut cake horizontally two times, creating three cake layers.
For the topping, beat whipping cream with powdered Swerve or powdered sugar. Frost first layer of cake with whipped cream, then add sliced strawberries. Repeat for second layer, then frost the entire cake with whipped cream. Add strawberries on top, if desired. Refrigerate for 1-2 hours before serving. Store covered in refrigerator for up to 3 days.