Gradient Orange Upside-Down Pie

Ingredients:

The top

• 5 Meyer lemons, zest of 1 lemon for pie crust
• 3 sweet Washington Navel oranges
• 5 tangerines
• 3 Moro blood oranges, zest of 1 orange for the dough
• 3 red American Ruby grapefruits
• 3 red Sicilian oranges
• Equipment: baking tray measuring 22 x 32 cm.

Syrup

• 1/4 cup granulated sugar
• 2 tbsp. l. brown sugar
• 1 tbsp (15 g) butter
• 1 tbsp. water

Sponge cake with sour milk

• 2 cups premium flour
• 2 tsp baking powder
• 1 teaspoon of baking soda
• 1/4 teaspoon salt
• 3/4 cup softened butter
• 1 and 1/4 cups granulated sugar
• 3 large eggs at room temperature
• 1.5 tbsp. sour milk
• 1 tsp vanilla extract

Preparation:

1. Preheat oven to 170°C.
2. For the citrus topPeel the lemons, oranges, and grapefruit and slice them into 0.7 cm thick slices. Use a 4 cm measuring rod to cut squares from the citrus fruits. Carefully arrange the slices on a baking sheet in a single layer; this will be the top of the pie, so be sure to follow the gradient. Starting with the blood oranges in the upper right corner, pack the slices tightly and rotate them at the corners to create diamond shapes.
3. Fitting the second row tightly into the "grooves" of the first row, arrange the citrus fruits by color, moving from dark to light, laying out two rows of each color until you've filled the entire space. Cut the remaining citrus diamonds in half and finish laying them out around the perimeter, filling the remaining "grooves." You should have a neat border.
4. For the syrupPlace the sugar, brown sugar, butter, and water in a small saucepan and bring to a gentle simmer over medium heat; cook until the sugar dissolves. Drizzle the syrup over the citrus fruits and, using a pastry brush, spread it evenly over the fruit.
5. For the sponge cake with yogurtPlace the flour, baking powder, baking soda, and salt in a bowl. In another bowl, combine the butter and granulated sugar and beat with a hand mixer until fluffy. Add the eggs one at a time and beat until combined. Add the dry ingredients to the wet ingredients and beat until smooth. Add the sour milk and beat until the batter is thick and lump-free. Stir in the vanilla extract and citrus zest until combined.
6. Pour the batter over the citrus fruits and spread it evenly with a spatula. Bake the pie for 30-35 minutes, or until a toothpick inserted into the center comes out clean and the top is golden brown. Remove the pie from the oven and let it cool for at least 30 minutes.
7. Cover the pie with a cutting board and invert it quickly but carefully. Slice it on the board and place it on a serving platter. Carry the orange upside-down pie to the table.
   
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