“An easy approach to the base of Flattop's East face.”
— Condor77 77
From the Bear Lake parking area (there will be great signage and there should be a established skin track but one still needs to pay attention), skin-up and head out on the Bear Lake trail. You'll climb above Bear Lake (amazing views of Glacier Gorge and Lumpy Ridge) looking for the Flattop Mountain trail, take the Flattop trail west (left) and continue climbing through the trees.
The next trail junction you'll come to will be the Bear Lake-Fern Lake trail, stay to the right and continue on the Fern Lake trail. You'll continue along this trail for a little under 3/4 of a mile eventually reaching a clearing at the base of Flattop's East face. Pick your skin track and start climbing, enjoy.