Start by crushing the 32 Biscoff cookies into fine crumbs in a food processor or zip top bag using a rolling pin. Mix with 5 tbsp butter until the texture feels like wet sand. Press the crumbs into a tart pan with removable bottom and push up the sides. Place on a rimmed baking sheet. Prebake for 10 minutes. Remove and cool.
Increase oven to 375ºF.
In a large bowl, whisk 4 large eggs, 1 cup brown sugar, 1/4 cup unsulfured molasses, 1/4 cup light corn syrup, melted 3 tbsp butter, 1 tsp vanilla bean paste, 1 tsp kosher salt, and zest of 1 medium orange in a bowl until smooth. Fold in 1 1/2 cups chopped pecans. Pour the mixture into the prebaked crust and spread evenly. Arrange 1 cup pecan halves on top outer edge in a circular pattern.
Bake until the filling is set at the edges and slightly wobbly in the center, about 45 minutes. Let the tart cool on a rack. Use a clean knife to get clean pieces.
Serve at room temperature. Add whipped cream or a small scoop of vanilla ice cream.