Chocolate fudge, the way my mother makes it

Some of my earliest food memories include the gooey chocolate fudge that my mother used to make. Deep brown, with slivers of creamy cashewnuts adding texture. They would be prefect diamonds, and each was guaranteed to transport your into food heaven.
When I started cooking, one of the first recipes I asked my mother for was fudge. She told me it was one of the easiest things to make, but she counted without me. I have made it about half a dozen times, and most of them have been disasters of various kinds. Sometimes, I don't let the sugar syrup cook enough, sometimes I let it cook too much. The kids are picky about what they eat, so it has essentially meant me putting on additional calories.
BUT, I love it so much (and it tastes so amazing when it actually turns out the way it should), that I soldier on.

1 full cup milk powder
1 level cup sugar
4 tbsp cocoa powder
1 tbsp butter
1/3 cup water

Stir water and sugar on low heat till it achieves one string consistency.
While stirring, mix together milk powder and cocoa till well mixed (I normally sieve them together a couple of times).
Once one-string consistency is achieved, turn off heat, and add the dry mixture with constant stirring. Add butter, mix well and pour it onto a greased tray to cool.
I tried cutting it while it was still warm- big mistake- cut after it has cooled down.