1/2 tsp. dry yeast
1 oz. warm water
1 tbsp. sugar
1 tbsp. vinegar
1/2 tsp. salt
1 c. flour
1 c. milk, room temperature

Dissolve yeast in warm water. Add all ingredients in a bowl and cover with plastic wrap. Let stand in warm place 2 days to ferment. It will become bubbly and have a sour smell. After second day, start your friendship bread or cake recipe.