Preheat oven to 375 degrees
In a stand mixture with a whisk attachment, beat the whites and cream of tartar until soft peaks form. Add the sugar and continue beating until stiff peaks form. This took many minutes, but was quite dramatic when it finally worked. Set aside and focus on the filling.
Whisk egg yolks in a medium mixing bowl. Set aside for a moment.
Which together in a saucepan then stir frequently over medium heat. Bring to a boil and allow to boil for one minute. In that minute, it will transform from a thin liquid to a thick, gloopy mass, which is pretty cool. Remove the heat.
One whisk at a time, transfer the hot gloop into the egg bowl, whisking constantly. When you’ve transferred about half, the eggs will be tempered and you can add the mixture back into the sauce pan. Stir constantly over low heat for a minute longer. Remove from heat.
Whisk in butter, lemon juice and zest.
Place 9 to 12 ramekins on a cookie sheet (exact number will depend on the sizes you have). Add the lemon filling into each ramekin until they are all filled evenly. Top with the meringue you made earlier.
Place in oven 8 to 10 minutes, until meringue has a nice, golden color. Remove from oven and carefully transfer ramekins to a rack to cool. Then, stand around drooling until they are completely cool. You want to eat them fairly quickly, as the lemon filling can separate form the meringue after a couple of days in the refrigerator (although they still taste really good!)