In a food processor, pulse the graham crackers with brown sugar until they form fine crumbs. Drizzle in melted butter while the processor runs until the mixture resembles wet sand. Firmly press this mixture into a greased 9-inch pie dish, spreading evenly across the bottom and up the sides. Place the crust in the freezer for 15–20 minutes to set.

In a large mixing bowl, whisk together the cold milk, green food coloring, and mint extract until fully combined. Once mixed, add the instant vanilla pudding mix, whisking vigorously for 2–3 minutes until the mixture thickens and becomes creamy. Allow it to sit for an additional 5 minutes.

Gently fold the thawed whipped topping into the pudding mixture using a spatula until no white streaks remain.

Spoon the creamy filling into the prepared graham cracker crust, smoothing the top with a spatula. Cover the pie with plastic wrap and place in the freezer for a minimum of 6 hours or overnight to set firm.

Before slicing, let the Shamrock Shake Pie sit at room temperature for about 5–10 minutes for cleaner cuts. Garnish with whipped topping or crushed mint candies if desired.