Preheat the oven to 350°F (175°C). In a medium bowl, mix graham cracker crumbs, 1/4 cup sugar, and melted butter until the texture of wet sand. Press evenly into the bottom and up the sides of 6 ramekins. Bake for 8 minutes, until lightly golden. Cool completely on a wire rack. 2. While the crusts cool, make the lemon curd: In a small saucepan, whisk together eggs, 1/2 cup sugar, lemon juice, and lemon zest. Cook over medium-low heat, stirring constantly with a whisk, until the mixture thickens and coats the back of a spoon (about 6-8 minutes). Do not let it boil or the eggs will scramble. Remove from heat and stir in butter pieces until smooth. Strain through a fine-mesh sieve into a bowl to remove any cooked egg bits and zest. Let cool to room temperature, about 10 minutes. 3. Divide the lemon curd evenly among the cooled crusts (about 2 tablespoons each). Spread into an even layer. Refrigerate for at least 15 minutes to set. 4. Make the meringue: In a clean, dry bowl, beat egg whites and cream of tartar on medium speed until foamy. Gradually add 1/2 cup sugar, 1 tablespoon at a time, and increase speed to high. Beat until stiff, glossy peaks form and the sugar has dissolved (about 5-7 minutes). Beat in vanilla. 5. Spoon or pipe the meringue over the chilled curd, making sure to seal the edges to the crust. Use the back of a spoon to create peaks. 6. Toast the meringue with a kitchen torch until golden brown, or place under a preheated broiler for 30-60 seconds, watching closely to avoid burning. Serve immediately or chill for up to 2 hours.