Grease a pop-over baking tray (12 troughs, each containing approx. 60 ml). Line with strips of baking paper (each approx. 5 cm wide). Wash the limes hot, dab dry and finely grate the peel. Halve the limes and squeeze them.
For the dough, whisk 65 g butter and 100 g sugar with the whisks of the mixer for about 3 minutes until creamy. Stir in egg, egg yolk, milk, almost 1⁄3 lime zest and 2 tbsp. juice. Mix rice flour, flour, 1 pinch of salt, baking powder and baking soda and fold in.
Pour the dough into the prepared bowls. Let rest for about 15 minutes. Preheat the oven (electric cooker: 175 °C/circulating air: 150 °C/gas: see manufacturer) and bake the cakes in the hot oven for 15-20 minutes (stick test!).
Take out and let it cool in the mould for about 5 minutes. Remove from the troughs and leave to cool on a cake rack.
For the caramel, meanwhile caramelise 50 g of sugar until golden. Deglaze with the rest of the lime juice. Simmer for approx. 5 minutes until the caramel has thickened a bit. Add the rest of the lime zest. Spread the caramel on the still slightly warm cakes, dust with icing sugar and serve immediately.