Preheat oven to 350 degrees F (175 degrees C). Lightly grease a 9 inch pie plate.
Whisk together egg, melted butter, and vanilla in a large bowl. Puree about 1/4 cup of the sliced strawberries and whisk into the butter. Sift together the sugar, cocoa powder, and cake flour. Fold into the butter, and mix until well incorporated. Use more flour if needed to end up with a mixture in between a cake batter and a cookie dough (the strawberries will add additional moisture). Gently fold in the remaining sliced strawberries and pour the batter into prepared pie plate.
Bake in preheated oven until a toothpick inserted into the center comes out clean, 30 to 40 minutes.
