Dissolve yeast in warm water in a small bowl. Beat eggs and egg yolk together in a small bowl. Scoop out 2 tablespoons of beaten egg; keep refrigerated.
Preheat the oven to 170 degrees F (75 degrees C).
Combine sugar, margarine, and salt in a large bowl. Mix thoroughly until dissolved. Add warm and cool cream to the bowl. Stir in yeast mixture. Beat in eggs. Add flour 1 cup at a time, blending well between additions.
Turn dough out onto a floured board; knead until smooth and elastic, 5 to 7 minutes. Spray a clean bowl with cooking spray. Place dough inside and spray the top.
Cover dough with a dish cloth. Turn off oven and place dough inside. Allow to rest until doubled in size, about 1 hour.
Remove dough from the bowl and knead for 2 to 3 minutes. Split in half; split each half into thirds. Roll each section of dough into long, 24-inch snakes. Braid 3 together, making sure to secure the ends. Repeat with the remaining 3 sections.
Reheat the oven to 170 degrees F (75 degrees C). Line a cookie sheet with parchment paper. Transfer braids to the cookie sheet.
Turn off oven. Let braids rise in the warm oven for 45 minutes.
Remove braids from the oven and brush with reserved beaten egg. Preheat the oven to 350 degrees F (175 degrees C).
Bake braids in the preheated oven until tops are golden, 25 to 30 minutes. Cool completely before slicing.