- With the rack in the middle position, preheat the oven to 350°F (180°C). Line a baking sheet with a silicone mat or parchment paper.
- In a bowl, combine the flour, matcha and salt.
- In another bowl, cream the butter and sugar with an electric mixer for 1 minute. Add the egg and vanilla. Mix until smooth. With the machine on low speed, or with a wooden spoon, stir in the dry ingredients.
- Transfer the dough to a pastry bag fitted with a 1/2-inch (1 cm) star tip. On the baking sheet, form the cookies by piping a series of four dots in a line, each dot about 1/2 inch (1.5 cm) in diameter, letting the four dots touch one another.
- Bake for 16 minutes or until the edges of the cookies are lightly golden. Let cool completely.
- Using a small spoon, cover the tip of each cookie with the melted white chocolate and top with the sprinkles, varying the colours, if desired