Preheat oven to 350 degrees F. Line a cookie sheet with parchment paper and set aside.
In a mixing bowl, beat the softened butter and granulated sugar together until light and fluffy, about 3 minutes. Add in eggs and 0.5 teaspoon almond extract, beating until combined.
Add the all-purpose flour, baking powder, and kosher salt to the batter. Mix just until well blended.
Using a 2 Tablespoon cookie scoop, drop cookie dough onto the prepared cookie sheet.
Bake for 12 to 14 minutes, until edges of cookies are firm and bottoms are lightly browned. Remove from oven and cool on pan for 10 minutes, then transfer to a wire rack and cool completely.
For the glaze, whisk powdered sugar with 0.25 teaspoon almond extract and milk until smooth. Drizzle over cooled cookies and sprinkle with sliced almonds.
Notes
These almond biscotti store well in an airtight container for up to one week. They also freeze beautifully before glazing.