Preheat the oven to 350 F (180 C)
Whisk the egg whites together with the cream of tartar and salt. Continue to whisk whilst gradually adding in 1/2 cup of the sugar. Beat until the egg whites hold stiff peaks, then whisk in the vanilla and almond extracts. Sift the flour and remaining sugar into the bowl. Also add the coconut to the bowl. Fold it all together with a rubber spatula until just mixed.
Pour the batter into an angel food cake/bundt cake / tube pan (if you use a bundt pan, I'd say you should grease it or make sure it's non-stick). and bake for 20-30 minutes. Leave to cool upside-down, on a wire rack. Once cool, loosen the edges with a palette knife and turn out onto a serving plate.
For the frosting, stir together 1/2 cup of the yogurt with all the powdered sugar and vanilla extract. Frost the cake with this, then use the additional yogurt to spoon + swirl on top. Decorate with your choice of toppings.