Place milk in a medium saucepan and heat over medium heat until it begins to steam and form a skin on top. Do not boil. Cool 10 to 15 minutes or until it is between 110 and 115 degrees.
Dissolve yeast in lukewarm water and let sit for 5 minutes. (Try and time this so it will be ready at the same time the milk reaches the correct temperature.)
Melt butter in microwave and cool 5 minutes.
In a large bowl, whisk together eggs, sugar, salt, and melted butter.
Whisk in cooled milk and yeast mixture.
Add flour 2 cups at a time, stirring in with a wooden spoon. Do not work the dough too much. Once the flour is mixed in, transfer the dough to a large bowl coated with vegetable oil. Cover loosely with plastic wrap and let rise until doubled in size, about 1-2 hours.
Punch dough down, cover with plastic wrap again and refrigerate for 4 hours to overnight.
After refrigerating, grease a 12x17-inch baking sheet with butter or cooking spray.
Make filling. Combine all filling ingredients in a saucepan and cook over medium heat, stirring frequently until some of the blueberries burst and the filling thickens some, about 5 minutes. Let cool some.
Lightly oil your hands and shape dough into approximately 2 1/2-inch balls. You should have 20 balls. Place balls on baking sheet, spacing 4 across and 5 down. Using your fingers, make a dent in the middle of each ball for the filling. Place about 1 tablespoon of filling in each one.
Cover loosely with plastic wrap that has been coated with cooking spray. Let rise until almost doubled in size, about 1 to 1 1/2 hours.
Preheat oven to 375 degrees.
In a small bowl combine butter, flour, and sugar for streusel. Use your fingers to mix the butter in well. Sprinkle on top of kolaches and bake for 25 to 30 minutes, until lightly browned.