Combine the ginger snaps and butter, add them to an 11-inch tart pan, and then freeze the mixture for about 15 minutes.
Let it bake for about 10 minutes, and then let it cool for about 10 minutes.
Reduce the heat to 325℉.
Whisk together the yolks, sugar, milk, ricotta, juice, and zest, and then add the mixture to the crust.
Let it bake for about 30 minutes, and then refrigerate it for about 3 hours & 30 minutes.
Notes
Press the ginger snap mixture into the bottom of the pan and up the sides. We use regular limes when key limes aren't in season, but you can use either!