Preheat the oven to 180°C.
Whip the egg whites with the cream of tartar until foamy, then gradually pour in 100g of the sugar, whipping until the whites hold a medium peak when the beaters are lifted. Set aside.
In a separate bowl, sift the flour, the remaining 100g of sugar, the baking powder and salt. Add the oil, egg yolks, lemon zest and juice and then, using electric beaters or a stand mixer fitted with the whip attachment, whip this on high speed until it is thick, pale and almost double in volume, about 3 minutes.
Using a whisk, fold a third of the whites into the flour mixture until almost blended, then fold in the remaining two thirds until evenly incorporated. Fill a piping bag (with no tip) or use 2 spoons to fill 48 ungreased mini-muffin cups with the batter, filling each cup about 3/4 full. Bake the mini cakes for 16 to 18 minutes, until the cakes spring back when gently pressed. While cooling the cakes, invert the tins so they are upside down (you can rest them on ramekins, so that air can circulate underneath them).
To remove the cakes from the tins, run a small palette knife around the cake and gently pop each out. Place these upright on a cooling rack that is resting over a parchment-lined baking tray.
To prepare the glaze, stir 200g of the sugar and the lemon juice over medium heat until the sugar has dissolved and the mixture just comes up to a simmer. Remove the pot from the heat and set aside to cool 15 minutes.
Stir in the remaining sugar (this will help create the crystal effect when the glaze sets). Spoon or brush each mini chiffon cake generously with the lemon glaze, ensuring that the tops and sides are covered. If you wish, top each mini cake with a little candied flower or silver dragée. Let the cakes set for at least 2 hours before serving or storing in an airtight container.
The mini chiffons will keep for up to 2 days in an airtight container (do not refrigerate or freeze).