Preheat the oven to 170 degrees C. Grease and flour a large baking tray.
In a large bowl, cream butter and sugar until light and fluffy. Beat in eggs, vanilla, almond essence and zest. Combine flour, baking powder, nutmeg and salt. Stir into the creamed mixture until just blended. Mix in almonds. Divide dough into two pieces. Form into long flat loaves about 1cm tall and 30cm long. Place the loaves 5cm apart on the prepared baking tray.
Bake in preheated oven for 25 minutes, or until a light golden brown. Cool on a wire rack for 5 minutes.
With a serrated knife, cut diagonally into slices about 1cm thick. Lay the slices flat on the baking tray. Bake for 10 minutes, turning over once. Transfer to a wire rack to cool.
Place chocolate chips into a small microwave-safe bowl. Melt chocolate in the microwave stirring every 20 to 30 seconds until smooth. Use a spatula to spread chocolate onto one side of each cookie. Let stand at room temperature until set. Store biscotti at room temperature in an airtight container.