Green’s Dictionary of Slang

hot cross bun n.

(Aus.) the sun.

1905		Duke Tritton’s Letter n.p.: The Hot Cross Bun was down and the Silver Spoon was rising when I spread the Wagga and turned in.
1931		E. Blair letter 4 Sept. in Complete Works X (1998) 228: I had thought that the ‘rhyming slang’ was quite extinct, but one occasionally hears it [...] ‘the hot cross bun’ for the sun, etc.
2002		Pete’s Aussie Sl. Home Page 🌐 hot cross bun: the sun.