Preheat oven to 350F. Lightly grease and flour a 9-in cake pan. Set aside.
Place egg whites in a large bowl. Using a handheld electric mixer, beat egg whites on high speed until stiff peaks form. Set aside.
In a large bowl, beat butter and sugar until creamy. Beat in egg yolks, agave, yogurt, milk, and vanilla until smooth. Combine flour, baking powder, and salt and then gently fold into liquid mixture until just combined. Very gently fold in whipped egg whites.
Scrape batter into prepared pan and smooth top. Bake cake at 350F 30-35 minutes or until a toothpick comes out with moist crumbs sticking to it. Cool completely in pan on a wire cooling rack.
In a medium bowl, mash 1-1/2 cups strawberries. Add remaining sliced strawberries and sugar. Let stand 10 minute until berries release their juices.
Once cake is cooled, run a knife around edges and invert onto a serving plate. Spread whipped cream over top of cake and top with strawberry sauce. Slice cake and serve immediately after assembling. Enjoy!