Can I use another brand of malted milk powder if I can't get Horlicks? (I'm not in the UK).
Nigella's Chocolate Malteser Cake (from FEAST) is a malted chocolate-flavoured cake. Nigella uses Horlicks, which is a malted milk powder. Ovaltine Classic Malt or Nestlé/Carnation Malted Milk Powder (Original) would be good alternatives and are available internationally.
Other brands are also available but vary by country. When using a substitute malted milk powder (and also for the Ovaltine, Nestlé and Horlicks), make sure that it is the type that is added to milk, and not the "instant" type where you add hot water to the powder. The instant powders have a different quantity of sugar and milk powder. It should also be the plain, "classic" or "original", variety of malted milk powder. Ovomaltine and Milo are both chocolate-flavoured malt powders and they contain cocoa and also more sugar than regular malted milk powders. If one of these is the only option available then you can try it, but unfortunately we have not made the cake with chocolate malt powder and so are unable to guarantee the results.