In a mixing bowl, whisk in the all-purpose flour together with the lemon zest and sugar. Make a well, add the eggs, lukewarm milk, spring water, rum, orange blossom water, and cooled butter. Start mixing from the center going outwards taking a little bit of flour at a time. NOTE: This is the secret to get a batter with no lumps!
1.76 oz granulated sugar, 8.81 oz all-purpose flour, 4 eggs, 14.11 oz milk, 3.53 oz spring water, 1 Tbsp Rum, 1 Tbsp orange blossom, 1 lemon zest