Toasted Pecan Torte with Butterscotch Topping

Place a rack in middle of oven; preheat to 350°F. Butter and flour pan. Toast pecans on a rimmed baking sheet, tossing once, until slightly darkened in color and fragrant, 12–15 minutes. Let cool.
Pulse baking powder, 1 tsp. salt, 1 1/2 cups flour, and 2 1/2 cups pecans in a food processor until nuts are finely ground. Using an electric mixer on medium-high speed, beat granulated sugar, orange zest, and 1 cup butter in a large bowl, scraping down sides, until light and fluffy, about 5 minutes. Add eggs to bowl. Beat until combined and mixture is even fluffier, about 1 minute. Beat in 3 Tbsp. rum; stop mixer and add dry ingredients. Mix on low speed just until combined, then fold a few times with a rubber spatula, scraping bottom and sides of bowl, to ensure batter is evenly mixed. Scrape batter into prepared pan and smooth top.
Bake torte until golden brown and a tester inserted into the center comes out clean, 45–50 minutes. Transfer pan to a wire rack and let torte cool in pan.
Meanwhile, bring brown sugar, 1/2 cup cream, remaining 1/4 cup butter, and remaining 1 Tbsp. rum to a boil in a small saucepan over medium heat, stirring often, and cook until slightly thickened, about 3 minutes. Remove butterscotch from heat and stir in remaining 3/4 tsp. salt. Mix in remaining 2 cups pecans and let sit at room temperature, stirring occasionally,until butterscotch is cool but still pourable.
Spread topping over torte. Whisk remaining 1 cup cream in a large bowl to medium peaks. Serve torte topped with dollops of whipped cream.
Topping (without pecans) can be made 3 days ahead; cover and chill. Reheat over low before mixing in the nuts. Torte can be baked 1 day ahead; store tightly wrapped at room temperature.