No point in mentioning Yellowman without quoting the lines in which it is mentioned in the song:”The Ould Lammas Fair”

“Did you treat your Mary Ann to Dulse and Yellowman
At the Ould Lammas Fair in Ballycastle O ”

I am going to give you the recipe direct from Darina Allen.

30g (1 oz.) Butter
2 Tablespoons Water
225g (8 oz.) Brown Sugar
450g (1 lb.) Golden Syrup
1 teaspoon Bread Soda.

Melt the butter in a heavy bottomed saucepan.
Add the water, sugar and syrup and stir until the sugar has melted.
Boil steadily until you get to 285C.
(When a little of the syrup will crack in cold water)
Stir in the sieved bread soda and pour it immediately on to a greased marble slab or baking sheet.
Turn the edges into the centre and continue to work it until the colour pales to yellow.
Leave to cool and break off pieces as you want.