Center the oven rack and preheat the oven to 350°F (180°C).
Line a baking sheet with parchment paper or a silpat.

Combine the flour, baking powder, and salt. Add the corn flour and mix again. Set aside.

Cream the butter and sugar at medium speed for 3 minutes, adding the eggs one at a time, beating between each addition, until the mixture is light and creamy.
Add the almond extract and mix.

Reduce the mixer speed and add the dry ingredients, mixing just enough to incorporate them.
Add the sliced almonds and mix.

Divide the dough into two equal parts and shape each part into a rounded rectangle, 12″ (30cm) long and 1 and 1/2″ (3.5cm) wide, and place each piece on the baking sheet.

Bake for 15 minutes or until the dough is golden brown and still soft to the touch.
Transfer the baking sheet to a rack and let cool for 30 minutes.

Preheat the oven to 350°F (180°C) again.

Using a serrated knife, cut into 3/4″ (0.8cm) slices.
Place the slices on the baking sheet and bake for 15 minutes or until the biscotti are golden brown and firm.
Transfer to a rack and let cool to room temperature.