Preheat oven to 350°F (175°C). Grease a 9×13-inch pan.
In a large bowl, mix cake mix, eggs, buttermilk, melted butter, and vanilla until smooth. Fold in toasted pecans.
Bake 30–35 minutes, until a toothpick comes out clean. Cool 10 minutes.
Poke holes over the cake using the handle of a wooden spoon.
For the praline sauce: Melt butter in a saucepan over medium heat. Stir in brown sugar and cream; simmer 2–3 minutes. Remove from heat, stir in vanilla and pecans.
Pour warm sauce evenly over the cake, letting it soak into the holes.
Cool completely before serving. Top with whipped cream or ice cream if desired.
Notes
Storage: Cover and keep at room temperature for 2 days or refrigerate for up to 5.