This split when I did it, but it’s probably worth another go as it tasted good.
220g dark brown soft sugar
1/4 teaspoon salt
6 tablespoons milk
350g sifted icing sugar
Melt butter in a saucepan, stir in the dark brown soft sugar and the salt. Bring to the boil and boil for 2 minutes, stirring constantly. Remove from heat and add the milk, stirring all the while.
Return to heat and bring to the boil again. Remove from heat and allow to cool until lukewarm (approximately 20 to 25 minutes). Stir in the icing sugar and beat until smooth and cool enough to spread. You might need to add a few drops of milk if frosting gets too stiff.