Martha makes rich, tender yeast dough with butter and sour cream.
In a small bowl, mix together yeast and warm water; set aside.
In the bowl of an electric mixer fitted with a paddle attachment, cream together butter and sugar on medium speed, scraping down sides of bowl with a spatula as necessary. Add egg yolks, one at a time, mixing well after each addition and scraping down sides of bowl with a spatula as necessary.
Add vinegar and vanilla; mix to combine. Slowly add sour cream, mixing until well combined. Add yeast mixture.
In a large bowl, whisk together both flours and salt. Add to mixer and mix on low until well combined and dough begins to pull away from the sides of the bowl and just begins to form a ball.
Turn dough out onto a lightly floured work surface. Knead dough until smooth, about 5 minutes. Lightly flour the bottom of a large glass bowl; place dough in bowl and cover with a clean damp kitchen towel. Cover bowl tightly with plastic wrap; let stand until doubled in size, about 3 to 4 hours, or refrigerate overnight.