Peel and pit the avocado. In the bowl of a stand mixer fitted with the whisk attachment, beat the avocado and lemon juice until lightened in color, 2 to 3 minutes. Add the powdered sugar, a little at a time, and beat until smooth. Add the lemon extract and mix to combine. Use right away or cover with plastic wrap, place in an airtight container, and store in the refrigerator for a few hours.