1.Preheat oven to 180°C/160°C fan-forced. Line 6-hole Texas (3/4 cup/180ml) or 12-hole standard (1/3 cup/80ml) muffin pan with paper cases.
2.Beat butter, flour, cinnamon, sugar, syrup and eggs in small bowl with electric mixer on low speed until ingredients are combined. Increase speed to medium, beat until mixture is changed to a paler colour.
3.Stir in nuts and grated apple. Divide mixture among cases; smooth surface.
4.Bake large cakes about 35 minutes, small cakes about 25 minutes. Turn cakes onto wire rack to cool.
5.Make maple frosting. Beat butter, sifted icing sugar and syrup in small bowl with electric mixer until light and fluffy
6.Make toffee. Combine sugar with the water in small heavy-based saucepan. Stir over heat, without boiling, until sugar dissolves; bring to the boil. Reduce heat; simmer, uncovered, without stirring, until mixture is golden brown. Remove from heat; stand until bubbles subside. Make toffee shards on baking-paper-lined oven tray.
7.Spread cakes with frosting; decorate with toffee shards.