Preheat the oven to 350 degrees Fahrenheit. Oil a bundt cake pan.Zest the oranges, then peel them and deseed if necessary. Blend the orange segments until you have a thick puree. You should have a cup of the puree.
Add the orange puree and zest to a large bowl or the bowl of a stand mixer along with the sugar, vanilla, yogurt and the oils. Mix using a hand mixer or a whisk, or on medium speed in the stand mixer.
Add the almond flour to the bowl along with salt and nutmeg, if using. Then sift in the all purpose flour, cornstarch, baking powder and baking soda.
Mix with a spatula first to keep the flour from flying all over, and then for 20 seconds in the stand mixer or with a hand mixer. If using a whisk, stop as soon as the batter comes together. Scrape the sides and bottom of the bowl to make sure you don't have any dry streaks of flour.
Stir in the sliced almonds, if using.
Pour the batter into the prepared bundt pan and smooth with a spatula. This cake comes out fairly easily from the pan, once it has baked, but if you are new at this add a dusting of flour to the bundt pan after oiling it to ensure you can unmold effortlessly.
Bake the cake for 50 minutes or until a toothpick near the center comes out clean.
Let the cake stand on a rack for 10 minutes, then run a knife gently along the edges and the center tube of the pan. Place a plate on top and turn the cake upside-down quickly to unmold. You might need to tap gently on the pan.
Place the plate with the cake on the rack and continue to cool. Once it has cooled, dust with powdered sugar and serve.