Prepare the mold and the fizzy powder. Lightly grease your candy mold or silicone ice cubes tray with vegetable oil. Combine all the ingredients for the fizzy powder in a small bowl and set aside.

Make the first batch of sugar syrup. Put half of the caster sugar, half of the golden syrup and half of the cream of tartar in a small saucepan. Pour half of the water along the edges of the pan. Place the pan over low heat and stir until all the sugar has dissolved. Increase the heat to medium high and put a candy thermometer in the pan. Let the syrup boil, without stirring, until the temperature reaches 135°C (275°F). Immediately take the pan off the heat. Add half of the lemon extract, half of the citric acid and half of the food colouring to the pan. Mix with an oiled spatula. Carefully pour the hot syrup into the mold, filling each cavity half way.

Fill the candies. Add half a teaspoon of fizzy powder in each cavity. You can add more if you like your candies on the bitter side. Clean and dry your pan, candy thermometer and spatula thoroughly. 

Make the second batch of sugar syrup. Prepare another batch of candies with the other halves of the ingredients following the same method. Pour the hot syrup in the cavities, sealing the fizzy powder in the middle.

Cover the candies. Allow your lemon drops to cool and harden completely before removing them from the mold. Roll the lemon drops in a mix of powdered sugar and cornstarch to coat them and prevent them from sticking to each other. Individually wrap the caramels in cellophane. Place the lemon drops in an air-tight container.