Make the Ritz cracker crust. Add the crackers to a big bowl and crush with your hands. (I like to grab a handful and squeeze my fingers into a fist.) They should be finely crushed, but not like flour. Add the brown sugar and salt, and stir to combine. Add the butter and knead until the mixture is homogeneous.
Dump the mixture into a 9-inch pie pan and use your hands to pat into a compact crust. Stick in the freezer until it’s completely frozen and firm, at least 20 minutes. (If you want to make the crust in advance, wait until it’s firm, wrap it well with foil, and refrigerate for up to 2 weeks.)
While the crust is freezing, heat the oven to 350°F and make the peanut butter filling.
Combine the brown sugar and egg in a large bowl and whisk until smooth. Stir in the peanut butter with a rubber spatula until totally smooth.
Add the filling to the frozen crust. Use an offset spatula to spread it evenly, so it totally fills the pie. Sprinkle generously with flaky salt.
Add the pie to a rimmed sheet pan (this makes rotating it halfway through way easier) and bake for 35 to 40 minutes, rotating halfway through, until the crust is golden brown, and the peanut butter filling is starting to brown. (Less time results in a fudgier filling. More time yields something closer to a blondie.)
Let the pie cool at room temperature for 8 to 12 hours before serving. (You can cover it with foil after a few hours, or whenever it’s cool to the touch.)
Emma is the food editor at Food52. Before this, she worked a lot of odd jobs, all at the same time. Think: stir-frying noodles "on the fly," baking dozens of pastries at 3 a.m., reviewing restaurants, and writing articles about everything from how to use leftover mashed potatoes to the history of pies in North Carolina. Now she lives in Maplewood, New Jersey with her husband and their cat, Butter. Stay tuned every Tuesday for Emma's cooking column, Big Little Recipes, all about big flavor and little ingredient lists. And see what she's up to on Instagram at @emmalaperruque.