First, make the crust. Center a rack in the oven and preheat to 350 (F).
In a food processor, combine 10 ounces speculoos cookies, 1 tablespoon dark brown sugar, and 1 teaspoon kosher salt. Pulse together until coarse and well combined. While continuing to pulse, stream in 1/2 cup melted unsalted butter and continue pulsing until the crumbs come together in giant clumps.
Use a rubber spatula to transfer the crumbs into an ungreased 9-pinch tart pan with high sides and a removable bottom. Use your fingers and the back of your hands to press the crumbs onto the bottom and sides of the pan, creating an even layer. The bottom and sides of the crust should be around 1/4-inch thick.
Bake in the preheated oven for 8 minutes, then transfer to a wire rack to cool slightly while you make the filling. Be sure to keep the oven on!
Next, make the filling. In a large, heavy-bottomed pot over medium heat, combine 1 can pumpkin puree, 1/3 cup granulated sugar, 2 tablespoons dark brown sugar, 2 teaspoons ground cardamom, 1 teaspoon ground cinnamon, and 1/2 teaspoon kosher salt. Cook for 5 minutes, using a heatproof rubber spatula to scrape the bottom and sides of the pan frequently. The mixture should start to sputter around 2 to 3 minutes in — don’t be afraid, this is what you want! You’re trying to cook off as much water from the pumpkin as possible to prevent your pie from being full of holes and pockmarked with bubbles. By 5 minutes, the mixture should become thick and glossy.
Remove from heat and slowly stream in 1 can sweetened condensed milk while continuing to whisk the mixture. Continue whisking until the sweetened condensed milk is fully incorporated, before whisking in 2 large eggs one at a time, only adding the second egg when the first has fully incorporated into the mixture.
Once the eggs are fully incorporated, carefully pour the mixture into the prepared cookie crust shell. Bake for 35 to 40 minutes in the preheated oven, or until the edges of the filling have set. The filling may have bubbled and puffed slightly in the oven, but don’t worry — it settles down as it cools. You can use a knife to tap on the sides of the tart pan to test the filling; the middle should wobble slightly, but the edges should stay in the same place. Be careful not to overcook — it’s better to pull it out of the oven earlier than later, as the filling will continue to cook after it’s pulled out the oven. Transfer to a wire rack and cool completely until fully set.
Once the pie has completely cooled, it’s time to make the meringue topping. Once the cupcakes have cooled to room temperature completely, make the icing. In the bowl of a freestanding electric mixer fitted with a whisk attachment, combine 3 large egg whites and 1 teaspoon pure vanilla extract. Set aside.
Combine 1 1/2 cups granulated sugar, 1/4 cup water, and 1/4 teaspoon cream of tartar in a medium, heavy-bottomed sauce pot. Stir to combine and fit a candy thermometer to the side of the pot. Place over medium heat and cook until the mixture boils, thickens, and reaches 240 (F). Once the mixture reaches 240 (F), immediately pour it into a liquid measuring cup to prevent it from getting hotter.
Return to the egg whites and turn the mixer to medium speed. With the mixer on medium speed, slowly pour the sugar syrup into the egg whites, aiming for the side of the bowl rather than the whisk and egg whites. When all the syrup is added, turn the mixer to medium-high and whisk until the icing becomes shiny, thick, and holds a firm peak. This should take around 10 minutes — don’t whisk any longer than that, or the icing will become too thick to spread and pipe!
Transfer to a piping bag with a start tip and use immediately, piping a meringue pattern on top of the pie. Gently torch the meringue with a chef’s torch; be careful at this point, the meringue burns very, very quickly! Enjoy immediately.