Place the flour, sugar, yeast, and salt in a large mixing bowl and stir to combine.
Cut the butter into ⅛-inch thick slices, then toss in the flour mixture to coat, making sure each slice is separate.
Stir in the milk, a little at a time, until a stiff dough forms (you may have to knead the dough with your hands to get all the dry ingredients incorporated).
Flatten the dough into a disc, wrap tightly, and chill for one hour.
Sprinkle the work surface, dough, and rolling pin with flour and roll the dough out into a long rectangle.
Fold into thirds, like a letter.
Turn 90 degrees, then repeat the rolling, folding, and turning process 2 more times, dusting with flour as needed to prevent sticking.
Wrap and chill the laminated dough for another hour.
Divide the dough in half and roll each half into a rectangle shape about ⅛-inch thick.
Sprinkle with about 2 tablespoons of the filling mixture.
Roll into a long log, then flatten the log.
Split the log in half lengthwise.
Divide each half into 3 portions.
Roll each portion into a spiral, then place in the wells of a muffin tin, cut side up.
Cover lightly with plastic wrap and allow the pastries to rise for 1 hour, or refrigerate overnight.
Preheat the oven to 375 degrees F.
Bake until deeply golden brown (approx. 20 to 30 minutes).
Cool for 5 minutes, then coat the cruffins in the remaining cinnamon sugar.