Mix flour, sugar, baking powder, and salt in a bowl.
Cut in butter with a pastry blender or two knives until mixture has a fine, even crumb.
Stir in egg and enough milk to make a soft dough.
Turn onto a lightly floured surface and knead with fingertips 30 seconds.
Put dough on a greased baking sheet and pat or roll out into a 15x10-inch rectangle.
Spoon filling onto center of dough in a 2-inch wide, lengthwise strip.
Cut dough with a knife or a pastry wheel into 1-inch strips starting at the edge of a long side and cutting to within 1/2 inch of the filling.
Repeat on second side.
Braid the strips over filling by lifting one strip from each side and crossing diagonally in center.
Brush top with a mixture of 1 slightly beaten egg yolk and 1 tablespoon undiluted evaporated milk.
Bake at 375F 20 to 25 minutes, or until lightly browned.