Preheat oven to 400°F.

Lightly grease a 10-inch quiche or tart pan (or a deep dish pie plate)

Heat 1 tablespoon olive oil over medium high heat in a skillet, and sauté 1 onion (diced) until softened.

Add in the 6 ounces fresh baby spinach leaves and cook until just wilted (you may need to do this in batches if your skillet is too small). Season with salt and pepper to taste. Set aside to cool 5 minutes.

Whisk together 4 large eggs, 1/2 cup all-purpose flour, and 1/2 teaspoon baking powder. Whisk in 1 1/2 cups whole milk, then stir in spinach-onion mixture. Add pepper, mix well.

Pour egg mixture into quiche pan. Top with 1/2 cup feta cheese.

Place the 1/2 cup cherry or grape tomatoes halves on top, and press gently so only the surface is visible.

Bake for 25-30 minutes, or until center is set and the edge is golden brown - and pulling away from the pan.

Cool for 10 minutes.

Garnish with extra feta, and some fresh basil leaves (optional).

Slice, and serve.