Step 1

Dissolve sugar and gelatin in boiling water in bowl. Stir in lemon zest and juice. Refrigerate until mixture is thickened but not completely set, about 1 1/2 hours.

Step 2

Grease 13 by 9-inch baking dish with vegetable oil spray and coat with 1/2 cup ground crackers. Using stand mixer fitted with whisk, whip evaporated milkon medium-high speed until stiff peaks form, about 5 minutes. Transfer mixture to large bowl. Using clean, dry mixer bowl and whisk attachment, whip chilled gelatin mixture on medium-high speed until thickened and light lemon colored, about 4 minutes.

Step 3

Using large spatula, fold gelatin mixture into whipped evaporated milk until no yellow streaks remain. Transfer mixture to prepared dish and smooth top. Sprinkle remaining 1/2 cup ground crackers evenly over top. Cover and refrigerate until fully chilled and set, at least 4 hours or up to 24 hours. Serve.