Preheat Oven & Prep Pan: Preheat the oven to 350°F and butter / grease and line with parchment paper a 9-inch (23cm) round cake pan.Mix dry ingredients: In a medium mixing bowl, whisk together the flour, baking powder, and salt, set asidePrep the Orange: Cut the top and the bottom of the orange to remove its stalks. Then cut the orange into pieces without removing the peel but removing seeds. (For a pithless version - Zest the orange and place the orange zest in the bowl of a food processor. Cut away all of the white pith and discard along with any seeds from the flesh then slice and add the flesh to food processor.)Blend In Food Processor: Place the flesh in the food processor. Process or blend the oranges until finely ground and the consistency of apple sauce.To the bowl of the food processor with the orange mixture, add the oil, sugar, vanilla and eggs and process until well combined, scraping down the sides of the bowl once or twice.Add the flour mixture to food processor and process together until the batter is just combined. No need to over mixBake: Pour and spread the batter evenly into the prepared cake pan and bake for 45-50 minutes, until a wooden skewer or toothpick inserted into the center comes out clean. Let cool on a cooling rack for 10 minutes before releasing the sides of the pan to let cool completely.Frost/Glaze: Once the cake is cooled make the glaze. In a small bowl or medium bowl whisk all the glaze ingredients until smooth adding a little more milk or cream as needed to reach desired consistency or to taste then spoon over or drizzle over cake. Let set before servingServe: Slice and serve with some whipped cream or even ice cream. Store leftovers in an airtight container at room temperature for up to 3 days.