Position a rack in the lower third of the oven and preheat the oven to 350°F. Grease and flour two loaf pans. Mix the flour, baking powder and salt thoroughly in a large bowl and whisk together. Set aside.
In the bowl of a stand mixer (with the whisk attachment), beat the sugar, olive oil and orange zest on high speed until well blended. Add the eggs one at a time, beating well after each addition; continue to beat until the mixture is thick and pale, 3 to 5 minutes. Stop the mixer and add 0ne-third flour mixture; beat just until combined. Add half of the sherry. Beat just until blended. Repeat with another third of the flour, followed by the remaining sherry, and then the remaining flour.
Scrape the batter into the pans. Bake until the cake tester comes out clean, 50 to 60 minutes. Cool the cakes in the pans on a rack for about 15 minutes before unmolding.
Slide a thin knife or spatula around the sides to release the cake. Invert the cake onto a rack. Turn the preferred side up before cooling the cake completely. Wrapped airtight, the cake keeps well at room temperature for up to 3 days, or freeze for up to 3 months.