Preheat the oven to 350 degrees Fahrenheit and line a cookie sheet with parchment paper.
In a medium-sized bowl, whisk together the oat flour, erythritol, matcha, baking powder and salt.
In a large bowl, whisk together the coconut oil, almond milk, vanilla extract, butter flavor, stevia extract and almond extract.
Dump the dry ingredients over the wet ingredients and fold together. Fold until the mixture can form into a dough ball (it will look sticky at first, but then the oat flour will absorb the liquid and turn into a play-doh/cookie dough texture).
Use a medium cookie scoop to portion out the dough onto the prepared cookie sheet. Roll the dough portions into balls, then use your fingers to press them into patties. Form them just a tiny bit thicker and smaller than you prefer your cookies -- they spread out a little. Bake for 12-14 minutes, or until baked through (when you tap the center of the cookie, it should be soft, but shouldn't leave a permanent fingerprint indentation).
Slide the parchment paper off the cookie sheet and let the cookies cool. Serve immediately, or transfer them to a freezer bag, seal tightly, and store in the freezer for up to one month. For a "freshly baked" cookie straight from the freezer, place a cookie on a plate and microwave for ~20 seconds!