Place egg white in a martini shaker. Shake vigorously until frothy, up to 5 minutes, and set aside.
In a pint glass with ice, mix the tequila, lemon juice, hazelnut liqueur and agave nectar. Add the mixture to the martini shaker with the egg white and shake to blend.
Strain and pour into a martini glass and top with chopped, toasted walnuts.
Recipe courtesy of Jill Davie