Heat oven to 350°F. Line a 9x13-inch pan with parchment and lightly grease.
Whisk milk, pudding mix, vanilla, and salt in a bowl until smooth, about 1 minute.
Pour the pudding mixture into the prepared pan and spread it into an even layer.
Sprinkle the dry cake mix evenly over the pudding layer. Do not stir.
Drizzle melted butter over the surface, aiming to moisten as much of the cake mix as possible.
Scatter chocolate chips and pecans over the top.
Bake 35–40 minutes, until the edges are set and the center is still a little gooey.
Cool 10–15 minutes before serving warm with ice cream or whipped cream.