In a large mixing bowl, stir together Biscoff cookies (1 pack) to a large mixing bowl, with the melted butter (6 tablespoons) and salt (1/4 teaspoon) until the mixture resembles wet sand.
Press the mixture into a 9” deep pie dish. Make sure to press the crumbs up the sides too. Use the bottom of a small glass or a measuring cup to press in firmly
Bake in preheated oven for 10-15 minutes. Remove to a wire baking rack and allow to cool completely.
Make Filling
Add the gelatin powder (5 teaspoons) and water (2 tablespoons) to a medium saucepan and mix together.Add the egg yolks (4), milk (3/4 cup), spices, sugar (2/3 cup), and salt (1 teaspoon).Cook over a medium heat, whisking constantly with a whisk, until thickened. The mixture needs to reach 170–175°F (77-79ºC). This will take about 10 minutes.Mix in the pumpkin (1 can), then allow to cool completely.
In a large bowl, using an electric mixer on medium speed, beat the egg whites until soft peaks have formed. Add the 1 tablespoon of granulated sugar and beat again until stiff peaks form.
Fold the egg whites into the pumpkin mixture until totally combined and airy.
Pour batter into the cooled pie crust and smooth evenly with a spatula.
Refrigerate for a minimum of 4 hours, or up to 12 hours.
In a large mixing bowl, using an electric mixer, beat the heavy cream (1 1/2 cups) with the powdered sugar (3 tablespoons) and vanilla (1/2 teaspoon), then spoon onto the pumpkin chiffon pie.
Notes
The egg-white question — here’s how my grandma taught me–My grandma always folded raw whipped egg whites into the cooled pumpkin custard — that’s the classic, old-fashioned chiffon method that gives this pie its iconic light and airy texture. If that’s how you grew up eating it, you’re in very good company. But if you have concerns — which are totally legitimate, especially for children, pregnant women, elderly guests, or anyone immunocompromised — there’s a safe alternative that keeps the texture just as dreamy: Heat the egg whites and sugar over a double boiler to 160°F, then whip and fold them in. This gives you the same chiffon lift with fully cooked whites.
Don’t rush the cool-down. If your custard is even slightly warm when folding in the egg whites, they’ll deflate instantly.
Chill longer for cleaner slices. Four hours is the minimum, but overnight gives you picture-perfect wedges.
Use real pumpkin purée. Pumpkin pie MIX has spices and sugar — not what you want here.