Preheat oven to 350˚F. Line a baking sheet with parchment or lightly grease.
In the bowl of a stand mixer fitted with a paddle attachment or a large bowl, beat butter and sugar until light and fluffy. Mix in the eggs, one at a time, followed by the vanilla.
In a medium bowl, combine flour, matcha, baking powder, and salt. Slowly mix into the butter mixture until just combined. Fold in the slivered almonds.
On the prepared baking sheet, form the dough into a 12 inch long log, about 1/2 inch thick and 3 inches wide. Reduce oven temperature to 275 degrees F.
Beat the egg in a small bowl and brush over the top of the log of dough. Sprinkle with the raw or granulated sugar.
Bake in the preheated oven until firm and golden on the bottom, 22-25 minutes. Allow to cool until able to be handled.
Reduce oven temperature to 275˚F. Use a serrated knife to cut the log on the diagonal into 1/2 inch thick slices. Arrange the slices back on the baking sheet, cut side down. Bake until crisp, 15-20 minutes. Flip the cookies to the other side and continue to bake until other side is crisp, another 15-20 minutes. Allow to cool to room temperature before storing in an airtight container for up to 2 weeks.