Preheat the oven to 350°F (180°C). Line the baking sheet with parchment paper or a silicone baking mat and set aside.
In a medium bowl, whisk together almond flour, all-purpose flour, baking powder, and salt until well blended.
1½ cups (150g) almond flour, ½ cup (60g) all-purpose flour, ½ teaspoon baking powder, ¼ teaspoon salt
In a stand mixer fitted with a paddle attachment, cream the butter, brown sugar, and vanilla on medium to high speed until light and fluffy.
½ cup (114g) unsalted butter, softened, ½ cup (100g) light or dark brown sugar, 1 teaspoon vanilla extract
Reduce the mixer speed to low and add the flour mixture. Mix just until the dough comes together, but do not overmix. The dough should be soft but not sticky.
If the dough feels dry or crumbly, add milk one teaspoon at a time until it reaches the right consistency. (I didn’t need to add any milk.)
Scoop out equal portions of dough using a small cookie scoop or spoon, then roll each portion into a smooth ball.
Arrange the dough balls on the prepared baking sheet, spacing about 2 inches apart. Gently press each ball to flatten slightly. Top the balls with sliced almonds, if you prefer.
Bake the cookies for 13-15 minutes, until they’re set and lightly golden around the edges but still soft in the center. The cookies will continue to firm up as they cool. For a crispier texture, bake a little longer.
Remove the cookies from the oven and let them cool on the baking sheet for 5 minutes. Then, transfer them to a wire rack to cool completely before serving or storing.