I started by making a buttercake from the Edmonds cake mix. I feel ashamed even admitting this because I don't usually like using packets for baking, but there's no denying it's a reliable and simple way to make a cake for decorating. (It's not half bad as far as taste goes, either.) If you are above packet mixes, try this recipe.
It's fairly easy to manipulate this kind of shape into an engagement ring, obviously:
The recipe I used for the icing was the Vienna Cream recipe:
125 g/4 oz butter at room temperature
1.5 cups icing sugar
2 T milk
Place butter in small bowl of an electric mixer and beat until it is as white as possible.
Gradually add about half the sifted icing sugar, beating constantly.
Add milk gradually.
Then gradually beat in the remaining icing sugar.
Mixture should be smooth and easy to spread with a spatula.
My flatmate's ring is white gold, with a sapphire in the middle and a diamond on each side of it. So it was easy enough colouring the icing for the stones - not so easy for the silver-coloured ring. I ended up choosing "gold" colouring for the ring, which turned out more yellow than gold. But never mind!
And then I made it more beautiful:
I felt pure happiness looking at my cake. I was also very proud when my cake was first choice for a number of children at the party.