In a bowl, add the butter and sugar, and beat well with a hand mixer until creamy.
Add the lemon zest and lemon juice, then sift in the flour and rice flour, and use your hands to bring the ingredients together into a dough.
Cover the bowl with clingfilm, and refrigerate for 30 minutes.
Transfer the dough to the work surface, and use a rolling pin to roll it to about half a cm or ¼ inch thickness.
Use a round cookie cutter or a glass to cut out rounds, depending on the size of your cutter you should get about 10-15 cookies.
Transfer the cookies to a large baking tray lined with non-stick paper, and bake in the preheated oven at 170 degrees Celsius (325 Fahrenheit) for about 25-30 minutes, or until slightly golden.
Remove from the oven and leave them to cool down completely.
Melt the white chocolate, add the lemon extract, and mix well.
When the cookies have cooled down, dip them into the melted chocolate - either all the way through or just half like I did.
Decorate with extra lemon zest if you wish.
Transfer the cookies onto a non-stick paper, and allow the chocolate to set completely before serving.