Blackberry Icing - Testing

Adapted from the Icing to Improve the Hips. I've made it with blackberry and with mixed fruit.

1 cup (8oz/228gr) softened salted butter

1⁄3 cup (2.8oz/78g)crème fraîche

1 Tbsp. vanilla

Grated zest of 1 lemon

2 to 4 cups (1 cup = 5.1oz/145g) icing sugar, sifted after measuring

1 to 2 Tbsps. of blackberry juice

1. Beat butter until creamy (it will become pale, almost white).
2. Blend in crème fraîche, vanilla, lemon zest and fruit juice; beat until very smooth.
3. Add the icing sugar.
4. Beat on high until smooth, no longer than 45 seconds or depending on the colour you want.