Preheat oven to 350°F Butter and flour an 8x8 inch square baking pan or a 9 inch round one and line the bottom with parchment paper. In a large nonstick skillet, cook 3 cups of the grapes and 2 tbsp of honey over medium high heat, stirring until liquid has mostly evaporated, approximately 10 minutes. Stir in the rest of the grapes and spread into the prepared baking pan In a medium bowl, whisk together the melted butter with the rest of the honey, the eggs, vanilla, almond extract and lemon zest. Whisk in the flour until batter is smooth and then pour batter over grapes and smooth surface. Bake for 25-30 minutes until toothpick inserted in the centre of it comes out clean. Let stand on cooling rack for 5-10 minutes then use a knife to loosen sides of cake and invert onto rack and let cool completely. Enjoy as is or dust with powdered sugar or with a dollop of whipped cream before serving.