- PREHEAT oven to 300F. Line a 9 × 13-in. non-stick metal pan with parchment, with overhanging edges.
- WHIRL flour with icing sugar, rice flour and salt in a food processor until combined. Add cubed butter through the feed tube while pulsing until dough just comes together. Dough will be slightly crumbly. Transfer to prepared pan. Press dough over bottom of pan. Use the flat bottom of a measuring cup to smooth the top. Score the surface into 24 squares, if desired. Prick dough all over with a fork.
- BAKE in centre of oven until top is just golden, 25 to 30 min. Cut shortbread into squares while still hot. Remove parchment and place on cooling rack. Keep in an airtight container at room temperature for several weeks.
Skor: Stir 2 chopped 39-g Skor bars into flour mixture. Continue with recipe.
Toblerone: Push a piece of Toblerone into each scored square before baking.
Lemon: Stir 1 tbsp lemon zest into flour mixture. Continue with recipe. Whisk 3/4 cup sifted icing sugar with 3 tbsp lemon juice until smooth. Lightly brush over cooled cookies, over a cooling rack. Excess icing will drip through the rack. Let stand 1 hour or until dry.
Chocolate: Instead of 1/3 cup rice flour, sift together 3 tbsp rice flour and 3 tbsp cocoa powder. Continue with recipe. Drizzle cooled cookies with melted chocolate.
From the kitchen of Julia Black (assistant home editor).
Cookie decorating: How to use royal icing