Preheat & Prep: Preheat oven to 350°F (175°C). Line a standard 12-cup muffin tin with paper or foil liners.
Make Crust: In a small bowl, combine graham cracker crumbs, ¼ cup granulated sugar, and melted butter. Mix until evenly moistened
Press & Pre-bake Crust: Press approximately 1.5 tablespoons of the crust mixture firmly into the bottom and slightly up the sides of each muffin liner. Bake for 5-7 minutes until lightly golden and set. Remove from oven and let cool slightly while preparing filling.
Make Filling: In a medium bowl, whisk the egg yolks until pale yellow. Whisk in the sweetened condensed milk until smooth.
Add Lime: Gradually whisk in the Key lime juice (and optional lime zest) until the mixture is fully combined and slightly thickened.
Fill Crusts: Pour the key lime filling evenly over the pre-baked crusts in the muffin liners, filling them nearly full.
Bake Pies: Bake for 12-17 minutes, or until the filling is set around the edges and the center is only slightly jiggly when gently shaken.
Cool Completely: Let the mini pies cool in the muffin tin on a wire rack for 20-30 minutes. Then, carefully remove them from the tin and let them cool completely on the wire rack.
Chill Thoroughly: Cover the cooled pies loosely with plastic wrap and refrigerate for at least 3-4 hours, or preferably overnight, until well-chilled and firmly set
Add Topping (Just Before Serving):For Whipped Cream: In a chilled bowl, beat heavy cream, powdered sugar, and vanilla extract until soft or medium peaks form. Dollop or pipe onto chilled mini pies.For Meringue: In a clean, grease-free bowl, beat egg whites and cream of tartar until soft peaks form. Gradually beat in granulated sugar until stiff, glossy peaks form. Pile or pipe meringue onto chilled pies. Optional: Briefly bake at 350°F (175°C) for 5-8 minutes or use a kitchen torch to brown the meringue. Garnish & Serve: Garnish with lime zest, thin lime slices, or toasted coconut if desired. Serve chilled.