- Heat oven to 350F and mist a 9″ round or square baking pan with cooking spray, and line the bottom with parchment paper.
- Thinly slice calamansi and discard the seeds. Place sliced fruit in a medium bowl with the granulated sugar, stir to combine, and let sit for 10 minutes. Add the water and olive oil; stir to combine.
- In another bowl, whisk together the flour, baking powder, baking soda, and salt. Add in the wet ingredients and mix until combined—a few lumps are okay—and pour into the prepared pan. Bake for 33-38 minutes, until the edges start to pull away from the side of the pan and a cake tester inserted into the center comes out with just a few moist crumbs.
- Once cool enough to handle, invert the cake onto a cooling rack to cool completely. Once cooled, dust with the confectioners’ sugar and a sprinkle of flaky sea salt. Keep leftovers wrapped tightly and store at room temperature up to a few days.
Note: Ripe calamansi are best for this recipe, so look for bright orange skin. A decent substitute would be kumquats, but I’d avoid larger citrus fruit like lemon or limes that contain more white pith—it would become too bitter.
— Recipe courtesy Holly Haines