For the dough, in a small bowl, stir the yeast and water together and whisk briefly to blend. Let sit 5-10 minutes. Then stir in milk, vanilla, eggs, sour cream and lemon juice. Meanwhile, in another larger bowl, cream the butter with the sugar. Blend in yeast/milk mixture. Then fold in salt, cinnamon, baking powder and flour to make a soft dough. Add in flour, as required to make a kneadable dough, and knead, about 5 minutes (not necessary to really work this dough – you want it smooth but not as elastic as a bread dough). Place dough in a well-greased bowl and cover with plastic. Let dough rest, until almost doubled, about 45 minutes. For the filling, blend all ingredients in a food processor until mixture becomes a thick paste. If too thick, loosen with more half & half. If not using right away, refrigerate. Warm up (at room temperature, stirring to loosen) to a spreadable consistency before using. You may have to add additional half & half or a touch of warm water at this point. Gently deflate dough and divide in half. Roll each section out into a rectangle, about 10 x 14-inches, thickness about ¼-inch. Spread on half of filling on each section; filling should be about 3/8-inch thick. Roll up in a jellyroll and place, seam side down, on baking sheet. Press roll down gently to flatten slightly. Brush each roll with beaten egg yolk and using a sharp knife, make several diagonal slashes on top surface. Cover with a damp tea towel and let rise briefly, about 20 minutes. Preheat oven to 350° F. Bake until nicely browned, about 25-35 minutes. Cool well, before cutting into serving sized pieces. Cover very well with plastic wrap to store as this will stale if not properly covered. Dust with confectioners’ sugar.