Special equipment: a 9-inch springform pan
For the cake: Preheat the oven to 350 degrees F. Line the bottom of a 9-inch springform pan with parchment and brush the sides with oil.
Combine the sugar, egg yolks and lemon zest in the bowl of a stand mixer fitted with the whisk attachment. Beat until very pale and thick and doubled in size. Reduce the speed and slowly beat in the olive oil and sherry. Gently stir in the flour using a wooden spoon just until combined.
In a second mixer bowl, beat the egg whites with a pinch of salt until they form stiff peaks. In three additions, gently fold the egg white mixture into the egg yolk mixture until just combined. Transfer to the prepared pan.
Bake until a cake tester comes out clean, 45 minutes. Let cool for 10 minutes. Remove the cake from the pan; let cool completely.
For the blueberry sauce: Combine the blueberries, sugar, lemon zest, cinnamon and 1/4 cup water in a saucepan. Bring to a simmer and cook until the berries have burst and the liquid has reduced to a jam consistency, 20 to 30 minutes. Remove the cinnamon stick and discard. Cool completely before serving.
Slice cake and serve topped with blueberry sauce and peaches.