'make the grated cheese more sticky'! The grated cheese should be melted into the sauce and then poured over the toast.
On the meaning of 'Welsh', place name dictionaries say it is from the Anglo-Saxon for 'foreigner', but this is not quite true. The word has pejorative connotations. For example --- my adoped hometyown in the UK's West Midlands is called WAlsall, derived from 'walsh heol', meaning 'the valley where the foreigners live'. This is because the invading English settled in all the towns around, but left the damp river valey to us Brits. A few miles north is a place called Eccleshall, which means 'valley where the Christians live'. Obviously by the time it was named the English colonisers had stopped calling the natives by the opprobrious 'walsh' and started to refer to them as Christians.
Regarding 'Taffy was a Welshman' --- H.B.Morton pointed out that it is an Anglicisation of an older Dutch Anti-Catholic sneer. You'll find it in either his 'In Search of England' or 'In Search of Wales'