Whisk together the flour, baking powder, salt and brown sugar. Next, using a pastry blender or your hands cut in the butter until it resembles coarse crumbs and no large chunks of butter remain.
In a small bowl combine the egg, milk, vanilla and almond extract and stir to combine. Add the wet ingredients to the dry and stir just until combined. Mix in the toasted almonds.
With damp hands, divide the dough in half and form into two rectangles about 3/4" thick on a parchment-lined cookie sheet. My rectangles were about 8" x 3".
To make the egg wash combine one egg yolk and 1 tbsp of milk. Brush the egg wash over the biscotti dough. Bake for 30-35 minutes or until lightly browned. Let the biscotti slightly cool.
Once it's cool enough to handle move to a cutting board and slice into 3/4"inch slices. Turn the slices on their sides on the baking sheet and bake again for 20 minutes, flipping halfway through. Cool completely.