1.Place whole unpeeled clementines in a large pot, cover with cold water and bring to a boil over high heat. Reduce heat to low, cover and simmer gently for 2 hours, adding more water as needed. Remove clementines with a slotted spoon and, once cool enough to handle, halve and remove any seeds or other hard bits. Purée in a food processor or blender and set aside. (May be done up to 2 days ahead and refrigerated).
2.Heat oven to 350 degrees. Spray a 9-inch springform pan with cooking oil, line bottom with parchment paper and spray paper with oil.
3.In a large bowl, whisk the eggs together with the sugar, salt and clementine purée. Add the almond flour and baking powder and stir until just combined. 4.Pour into prepared pan and bake until edges are golden brown and starting to pull away from sides of pan, about 1 hour. Transfer to wire rack set over baking sheet. After 10 minutes, run a knife around edge of pan to loosen cake; remove cake from pan. Peel off parchment paper and return cake to wire rack to cool completely. Decorate with dusting of powdered sugar, or with chocolate glaze and/or candied clementines.