• 1 teaspoon butter, softened, for the pan
• 1 1/2 cups all-purpose flour
• 2 teaspoons baking powder
• 1/4 plus 1/8 teaspoon kosher salt
• 1/2 cup buttermilk or 1/4 cup whole milk mixed with 1/4 cup plain yogurt
• 1/2 cup fruity extra-virgin olive oil
• 2 large eggs, at room temperature
• 1 cup granulated sugar
• 1 teaspoon grated orange zest
• 1 teaspoon grated lemon zest
• 1 teaspoon chopped fresh thyme leaves (optional)
• Confectioner's sugar
Preheat the oven to 350°F. Brush the inside of a 9-inch straight-sided cake pan with the butter. Spoon a teaspoon or two of flour into the pan and tilt it until it is completely coated. Invert and tap to release excess flour.
Place a sifter or a strainer over a bowl and sift together the flour, baking powder, and salt. Stir again with a fork and set aside.
In a measuring cup, mix together the buttermilk and olive oil.
Crack the eggs into a medium bowl and whisk until blended and frothy. Whisk in the sugar, orange, and lemon zest--and the thyme, if using--and beat until well blended, 1 minute. Beat in the dry ingredients in 3 batches, alternating with the milk-oil mixture, using as few strokes as possible. Pour the batter into the prepared pan.
Bake the cake 35 to 40 minutes until a tester inserted in the center comes out clean. Cool the cake on a rack 5 minutes, then invert onto the rack. Cool completely and invert onto a platter. Sift some confectioner's sugar over the top.