Preheat the oven to 180°C. Grease and line the bases of 8 mini loaf or muffin tins, depending on what you have.
Transfer to a large bowl. Add the yogurt and eggs and mix to thoroughly combine and there are no lumps or yogurt streaks remaining
Evenly distribute the batter between the lined tins to about 2/3 full. Tap to level off. Place on a baking tray and cook for 25 minutes, rotating the tray half way through to ensure they cook evenly, until a skewer inserted into the centre comes out with just a few crumbs, the cakes bounce back to touch and are starting to pull away from the sides of the moulds. Allow to cool in the tins for 15 or so minutes before removing to a wire rack (don’t leave in too long to avoid them sticking to the tins). Leave to cool completely.
Spoon chocolate ganache over the cakes and spread so it drips off the sides. Top with extra chopped toasted hazelnuts. Leave to set or serve immediately. Store in an airtight container for a few days.