Ukrainian Easter Paska

This recipe was handed down from my Ukrainian grandmother, and it is a long standing Easter tradition to make Paska every year.
Makes 2 large loaves with decorations, or four small loafs.

710g flour, unbleached all purpose
680g milk, scalded and cooled (or 630g water + 55g dry milk powder, scalding not necessary)
1 tsp yeast, dry active 
67g sugar, white
227g water, lukewarm

1278g flour, unbleached all purpose
1-1/4 tsp. yeast, dry active 
6 eggs, 1 separated and egg white reserved
135g sugar, white granulated
150g butter, unsalted
19g salt

2 Tbsp. water
1 egg white, reserved from above

This recipe requires a large 5-6 qt. stand mixer to knead. If you mixer is smaller, either divide the dough or do it by hand.

For the sponge: Combine yeast, sugar and lukewarm water. Allow to soften if yeast is not instant. Add milk, and flour and beat in a stand mixer (with paddle) or with a whisk until smooth (2 minutes in a mixer, 5 minutes by hand). Cover and allow to rise for 2 hours minimum, more time will aid in flavor development.

For the dough: Add sugar and eggs and mix until well combined. Add flour and butter cut into several small (1 Tbsp.) pieces. Mix on low (with dough hook) until ingredients are well combined. Allow dough to rest for 20 minutes, covered.

Add salt and knead on speed to 2 for 6 minutes. 

By hand: (Alternately, mix in sugar and eggs with a wooden spoon, then add flour and butter in small pieces until a loose dough forms and then turn onto a flour counter and knead by hand for 10 minutes.)

Cover and allow to rise for 1 hour. Punch down and rise again for 1 hour.

Divide dough into two equal pieces (for large rounds or four for small loaf-pans). Remove some from each piece for decorations. Shape loaves as desired. You can put them in loaf pans, or in round spring form pans for a more traditional look. Allow to rise for 1 hour. Roll out decorations and decorate loaves. A braided cross in the middle and a braid around the edges are traditional. There are lots of possibilities! Little snails look nice. You can use scissors to cut out leaves. Preheat oven to 400F. Rise for an additional 30 minutes.

Brush loaves with a mixture of 1 egg white 2 Tbsp. water. Bake at 400 for 15 minutes, reduce temperature to 350F and bake for an additional 40 minutes. Check halfway through baking, if the tops of the loaves are dark brown, cover loosely with foil and complete baking. Remove from oven and cool completely before eating.