Pre-heat oven to 350° F.

Finely grind oat flakes in food processor and put in a bowl. Add powdered sugar, vanilla extract, salt and butter and process into a dough. Wrap dough in plastic wrap and refrigerate for 1 hour. Then dust work surface with flour and roll out dough to ¼-inch thickness. With a cookie cutter or drinking glass, cut roughly 2-1/2 in diameter cookies and put them on a baking sheet, leaving some space between them. Bake 10-13 minutes or until edges are lightly brown. Move them carefully to a cooling rack.

Cut the white chocolate into pieces and melt in a bowl over hot water. Add the matcha powder and mix together. Finely chop pistachios. Cover each cookie with chocolate and sprinkle with pistachios.