Preheat the oven to 175 C. Line 10 muffins moulds with cupcake liners and set aside.
In a mixing bowl, combine the sugar and zest of both oranges. Use your fingertips to rub the zest into the sugar until it's a pale orange and slightly moist. This helps get a really nice orange flavour in the muffins!
Slice one of the oranges and squeeze out the juice to get 1/3 cup.
Add the eggs and beat on low-medium speed with a hand mixer for a minute or two, until pale and slightly thickened. Add the vanilla, orange juice, olive oil and yoghurt and beat briefly to combine.
Now fold in the ground almonds by hand, with a silicone spatula or spoon. Sift in the flour, baking soda and salt, and stir gently until just combined. Do not over-mix the batter.
Divide the batter equally among the muffin moulds, filling them two-thirds of the way (you may get an 11th muffin like I did, I prefer to not risk overflow and have an extra muffin, even if slightly smaller!).
Bake for 25 to 30 minutes, until browned on top, slightly domed (they will fall a bit as they cool and not have very tall tops), and a toothpick poked in the center comes out clean.
Allow the muffins to cool to room temperature because that's when they taste best. Store in an airtight tin for 2 to 3 days (the tops will soften once stored in a closed box) and in the fridge for a week, and the freezer for a few weeks. Happy baking!