Preheat oven to 325°F. Grease and flour Bundt pan, and drop crushed pecans into the bottom of the pan. Set aside.

In a stand mixer, cream sugar and butter together. Add flour, cornstarch, powdered milk, baking powder, kosher salt, and 3 tablespoons of oil; combine until evenly distributed.

In a separate bowl, whisk together eggs, milk, rum, vanilla, and remaining 1/2 cup vegetable oil. Add to the dry mixture; mix until combined. The batter should be smooth, thin, and pour easily.

Pour the batter into the prepared Bundt pan, and tap the pan on the counter to release air bubbles. Bake for 50–60 minutes, or until a toothpick inserted into the center of the cake comes out clean.

Let cake cool in pan for 10 minutes. Invert onto a cooling rack and let cool for another 20–30 minutes.

While the cake cools, prepare the rum sauce. In a small saucepan, over low heat, stir all ingredients together. Cook until thickened, stirring constantly for about 5 minutes. Drizzle over the cake, let set for 10 minutes, and serve.

In a small saucepan, whisk yolks and sugar until smooth. Warm cream and butter in a separate pan over medium-low heat until just steaming (160°F).

Slowly whisk hot cream mixture into yolks to temper. Cook over medium-low heat, stirring constantly, until thick enough to coat the back of a spoon, 6–8 minutes. Do not boil.

Remove from heat; whisk in rum and vanilla. Return to low heat for 1–2 minutes, stirring, until glossy and just steaming again. Let it sit 5–10 minutes to thicken slightly, then drizzle on cake and serve.