Step 1Heat oven to 350 degrees. Oil a 9-inch round baking pan and line the bottom with a round of parchment paper.
Step 2In a large bowl, sift or whisk together the flour, semolina, baking powder, salt and pepper.
Step 3In the bowl of a stand mixer, or in another large bowl, place the sugar. Very finely grate the zest of 3 of the oranges and add to the sugar, working over the bowl to catch any spray of citrus oil. Using a muddler or the back of a wooden spoon, mash together the sugar and zest until the sugar is moist and tinted pale orange and set aside. Juice 1 of the oranges and set aside.
Step 4Using a stand mixer fitted with the paddle attachment, or an electric mixer, beat the olive oil with the sugar-zest mixture over medium speed until well-blended. Add the eggs, one at a time, and beat just until the mixture is creamy. Beat in 1 tablespoon of orange juice and 1 teaspoon orange blossom water. On low speed, add the flour mixture in three batches, beating until just blended; be careful not to overbeat.
Step 5Pour the batter into the prepared pan. Bake the cake until the top is pale golden and springs back to the touch, and a toothpick inserted into the center comes out clean, 20 to 30 minutes.
Step 6Set the pan on a wire rack and cool for 5 minutes. Run a thin-bladed knife around inside edge of pan and turn out the cake onto rack to cool. Invert the cake onto a serving platter and wrap tightly until ready to serve. The cake may be made up to 1 to 2 days ahead. Wrap well and store at room temperature. (The cake can also be made and frozen, tightly wrapped, up to 2 weeks ahead.)
Step 7Prepare the orange garnish for the cake (this can be done up to a few hours before serving): Using a 5-hole zester, remove the zest from the remaining orange in long strands, allowing them to fall into a bowl as you work.
Step 8Peel and segment the 3 oranges: Slice the top and bottom off of the oranges, exposing the flesh. Stand the fruit on one end and shave off the peel and pith, tracing the curve of the fruit with your knife and rotating the orange after each cut. Stand the fruit on its opposite end and remove any additional peel and pith. Hold the fruit in one hand over the bowl and slice along both sides of each segment to free it from the membrane, dropping the segments into the bowl with the zest. Squeeze the membrane to extract juice. Stir in the reserved juice and remaining 1 teaspoon orange blossom water.
Step 9To serve the cake, spoon orange segments and juice over each slice. Top with pistachios, and a pinch of pepper. Drizzle olio nuovo over, then shave chocolate over using the large holes of a cheese grater. Alternatively, serve the cake plain and pass the topping components for the guests to garnish the slices themselves.