In a large bowl, combine flour, butter, and powdered sugar. Cut in butter using a pastry blender or your fingers until the mixture resembles coarse crumbs.

Add ice water, one tablespoon at a time, until the dough comes together. Form into a disc, wrap in plastic, and chill for 30 minutes.

Roll out the dough and cut out circles using a cookie cutter. Press into mini muffin tins. Prick the bottom of each crust with a fork.

Bake at 375°F (190°C) for 12-15 minutes, or until golden brown. Let cool completely.

In a saucepan, whisk together sugar and cornstarch. Gradually stir in water, lemon juice, and lemon zest.

Cook over medium heat, stirring constantly, until the mixture thickens and comes to a boil. Reduce heat and cook for 1 minute more.

Remove from heat and stir in butter and egg yolks until smooth.

Pour the lemon filling into the cooled crusts.

In a clean, dry bowl, beat egg whites with an electric mixer until soft peaks form. Gradually add sugar and cream of tartar, beating until stiff, glossy peaks form.

Pipe or spread the meringue over the lemon filling.

Bake at 350°F (175°C) for 8-10 minutes, or until the meringue is lightly browned. Alternatively, use a kitchen torch to brown the meringue.

Let cool completely before serving.