Squeeze the juice from 4 limes. Mix the juice with enough water to equal 200 ml (approximately 1 cup). Bring the juice and 200 grams (approximately 7 ounces) of sugar to a boil over high heat for about 20 minutes, until syrupy. Remove from the heat and let cool.
Line a muffin tin with paper cups.
(remove this step)
Mix the flour, baking powder, 100 grams (approximately 3.5 ounces) of sugar, sour cream, butter, lime syrup and the salt. Stir in the eggs. Mix until all ingredients are moistened.
Pour the batter into the muffin tin. Bake for about 20-25 minutes at 180°C (approximately 350°F).
Rinse the remaining limes.
Pat the limes dry and peel. Cut the shell into fine strips. Squeeze the juice. Mix the lime juice, shell strips and remaining sugar.
Remove the muffins from the oven and immediately sprinkle with the lime sugar. Let cool and serve.