Nutrition per serving may change if servings are adjusted.
1 large egg white
1 1/2 cups graham cracker crumbs, (12 whole crackers)
1 1/2 tablespoons butter, melted
1 1/2 tablespoons canola oil
2 cups nonfat vanilla yogurt
1 1/4 cups sugar
1/2 cup lemon juice
1 envelope plain gelatin, (2 teaspoons)
1/3 cup cold water
1 teaspoon freshly grated lemon zest
Yellow food coloring, (optional)
1/2 cup whipping cream
Lemon slices, and mint leaves for garnish
To make crust: Preheat oven to 350 °F. Coat a 9-inch pie pan with cooking spray. Whisk egg white in a medium bowl until frothy. Add graham cracker crumbs, butter and oil and blend with a fork or your fingertips until thoroughly combined. Press the mixture in an even layer on the bottom and sides of the pie pan. Bake until lightly browned, about 10 minutes. (Do not be concerned if there are small cracks.) Cool on a wire rack.
To make filling: Line a colander or strainer with cheesecloth or coffee filters and set over a bowl. Spoon in yogurt and let drain in the refrigerator until it measures 1 1/2 cups, 45 minutes to 1 hour.
Meanwhile, stir together sugar and lemon juice in a heavy nonreactive saucepan. Bring to a boil and cook over medium-low heat until the syrup reaches 239 °F on a candy thermometer (soft-ball stage), about 3 minutes. To be sure the syrup has reached the proper temperature, spoon a few drops into a glass of ice water; it should form a soft ball on the bottom of the glass. Remove the syrup from the heat and pour it into a mixing bowl.
Sprinkle gelatin over cold water in a small bowl. Let soften for 5 minutes, then whisk into the lemon syrup until completely dissolved. Set the syrup aside to cool for 1 hour. (Alternatively, set the bowl of syrup into a larger bowl of ice and stir occasionally until cool.)
Whisk the drained yogurt and lemon zest into the cooled syrup. Refrigerate until very cool, stirring occasionally, about 1 hour. (Or, again, stir over ice.) To enhance the color, add about 2 drops of yellow food coloring, if desired.
Whip cream in a chilled bowl until moderately stiff; fold into the yogurt mixture. Spoon the filling into the crust and refrigerate until firm, about 2 hours. Just before serving, garnish with lemon slices and mint sprigs.
Make Ahead Tip: Cover and refrigerate for up to 1 day ahead.