Cut up the plums in bite size pieces.
Combine the sugar and tapioca and sprinkle over the plums and let sit for 20 minutes.
Bring to a boil and cook on medium heat for about 5 minutes.
Cool the sauce and freeze in desired portion sizes.
To serve, thaw sauce and heat gently til warm.
Pour over vareniki and cream sauce.
On medium heat, melt the butter in a saucepan or frying pan.
Add the flour and stir together with a whisk cooking until the flour begins to change color.
Pour in the cream and milk and cook until bubbly, stirring frequently with the whisk to prevent lumps.
Add salt to taste.
When the sauce is smooth and thickened it is ready to serve, it takes about 3 minutes.
If you desire to use all cream or all milk that is just fine.
