Prepare yeast starter by mixing warmed milk (115F) with yeast, sugar and a third of the sifted flour
Whisk well and set it aside to rise for about 15 - 20 minutes. The yeast will start growing and bubbles will form.
Add eggs and remaining sugar and mix
Add flour in batches
By adding flour in batches, I make sure I do not add too much flour. I do not want the dough to become tough. The dough needs to still be a but sticky and easy to knead
Add melted and cooled butter
Knead by hand or mixer with a hook attachment until the dough is smooth and comes off your hand
Cover the bowl with a clean towel or plastic wrap and let it rise until it doubles in size. It usually takes 45 minutes but the time will vary depending on the climate you live in, how warm your home is. I live in warm South Florida and yeast dough doubles in size in my home pretty quickly. So, do not be alarmed if in 45 minutes your dough is not ready yet
Spread the dough into a well greased baking dish (9 by 13 inch)
Prepare crumble by mixing softened butter, flour, sugar and oats
Spread the crumble topping over the dough
Bake at 335 F for 30 - 40 minutes. The time and temperature may vary depending on your oven. You may have to dial it in like I had to. If the temperature is too high the cake will come out dark and dry. So when you bake it for the first time, make sure to keep an eye on it while baking