Combine milk and heavy cream and vanilla in a large bowl.
Add lime juice and .5 tbsp lime zest and whisk until thickened, about 1 minute.
Spread 1 cup filling on bottom of deep-dish pie plate, 11-inch oval casserole, or 2 shallow pie plates.
Top with single layer of Ritz crackers.
Repeat, alternating layers of filling and crackers until pie plate is full (finish with a layer of filling).
Sprinkle with 1 tbsp grated lime zest.
Refrigerate at least 2 hours or up to overnight.
Serve.
