Preheat the oven to 350 degrees.
In a food processor, grind the graham crackers and brown sugar until they are fine crumbs.
Add the melted butter and pulse until combined.
Press the mixture into the bottom of a 8x8 pan lined with parchment paper.
Place the pan in the oven and bake for 10 minutes.
Remove and let cool to room temperature.
In a large bowl, whisk the egg yolks, milk, zest, vanilla and salt.
Add in the lemon juice, and whisk until smooth.
Pour over the cooled crust and bake for 25-30 minutes, until the center is set.
Remove and let it come to room temperature before chilling in the refrigerator for 3 hours.
Sprinkle the top with powdered sugar and slice and serve.