This is something I had at a friend's house. I bet it could easily be made
in a pie pan if the recipe sounds similar to what your mom remembers.

LEMON CRUNCH

1 1/3 c. soda crackers, finely rolled
3/4 c. butter
1/2 c. granulated sugar
3/4 c. all-purpose flour
1/2 c. coconut
1 t. baking powder

Crumble all ingredients together. Remove 1 cup of crumbs for topping.
Press remaining crumbs into greased 9"x9" pan. Bake in 350 degree oven
for 15 minutes. Remove from oven and spread with filling.

Filling: 3 eggs, beaten
1 lemon, rind and juice
1 c. granulated sugar
1/4 c. butter

Beat eggs in top of double boiler or heavy pot. Add remaining
ingredients. Stir and cook until thickened. Spread over bottom
crumbs. Sprinkle reserved crumbs over top. Return to oven until
browned slightly. Cool. Cut into squares.