In a small bowl, beat butter and flour until combined; spread into a 12x6-in. rectangle on a piece of waxed paper. Cover with another piece of waxed paper; refrigerate for at least 1 hour.

In a large bowl, dissolve yeast in warm water. Add the milk, sugar, egg, salt and 2 cups flour; beat until smooth. Stir in enough remaining flour to form a soft dough. Turn onto a floured surface; knead until smooth and elastic, about 6-8 minutes.

Roll dough into a 14-in. square. Remove top sheet of waxed paper from butter; invert onto half of dough. Remove waxed paper. Fold dough over butter; seal edges.

Roll into a 20x12-in. rectangle. Fold into thirds. Repeat rolling and folding twice. (If butter softens, chill after folding.) Wrap in plastic; refrigerate overnight

Unwrap dough. On a lightly floured surface, roll into a 25x20-in. rectangle. Cut into 5-in. squares. Cut each square diagonally in half, forming two triangles.

Roll up triangles from the wide end; place 2 in. apart with point down on ungreased baking sheets. Curve ends down to form crescent shape. Cover and let rise until doubled, about 45 minutes.

Bake at 375° for 12-14 minutes or until golden brown.

To make Thai tea custard, mix egg yolk and sugar until well blended. Add coconut milk and thai tea. Stir under low heat and sift corn starch slowly. Keep at low heat until the custard become thicken.

To fill the custard inside croissant. At the bottom of croissant, use sharp knife to cut a small hole then fill the custard by using small tip piping bag.