Preheat oven to 375 degrees. Lightly spray a 9×13-inch baking dish with cooking spray.: The warm air of the oven should feel stable and steady before you place anything inside, you want a consistent environment so the crust begins to set immediately. You may notice a faint dryness in the kitchen as the oven comes up to temperature, which is normal. This heat is important because the quick initial bake of the crescent dough sheet helps it hold shape when the filling is poured in. A common mistake is rushing this step, putting the pan in while the oven is still cold which can make the crust soggy instead of lightly crisp.
Unroll crescent sheet and press it into the bottom of the prepared baking dish, pushing it up the sides a little bit. Bake for 5 minutes.: Look for an even sheen across the pan, this prevents sticking without pooling oil that could fry the edges. The lubrication ensures the bars release cleanly once cooled. If you skip this or apply too sparingly, you risk the crust adhering to the pan, making slicing messy and serving difficult. Wipe any excess spray from the rim so it does not burn and darken the edges during baking.
In a medium bowl, whisk together sugar, corn syrup, melted butter, vanilla and the egg.: As you press, feel for air pockets and smooth them out so the sheet sits flat and even, which helps the filling distribute uniformly. The dough should have a slightly tacky touch and will give a soft resistance when you press it into the corners. If you see tears, gently patch them by pressing dough back together, but avoid overworking it. Over handling can make it tough rather than tender.
Stir in pecans and chocolate chips.: You will see the edges barely start to color and the surface take on a faint sheen, this par bake helps the crust set so it does not become soggy under the filling. The brief time in the oven dries the surface and creates structural integrity. A common misstep is leaving it much longer which can overbrown the crust before the filling has a chance to set, leading to a tough texture.
Pour evenly on top of crescent dough crust. Bake for 18 to 22 minutes.: When these ingredients come together you should see a homogenous, glossy mixture that thickens slightly as the egg is incorporated. The aroma will be sweet and warmly reminiscent of caramel. Whisking thoroughly matters because it ensures even sweetness and prevents streaks of uncooked egg in the final bake. Avoid under mixing, which can lead to pockets of egg or uneven set, and also avoid overbeating which can introduce air bubbles that create holes in the finished bars.
Stir in pecans and chocolate chips: Fold the pecans and mini chocolate chips until they are distributed evenly, noticing how the mixture thickens and gains texture. The nuts will add a toasty aroma, while the chips sit suspended in the glossy filling. Take care to stir gently so chips do not melt into the batter prematurely and cause streaks of chocolate, unless you prefer that melty look. A frequent error here is overcrowding the mix with add ins which can make the filling too chunky to pour evenly.
Pour evenly on top of crescent dough crust: Watch as the filling glides across the par baked crust, filling crevices and evening into a level surface. The glossy mixture will spread and settle, and you may tap the pan lightly on the counter to remove small air bubbles. This even pour is important so every bar has the same ratio of crust to filling. If you pour too hurriedly you might displace the crust, and if you overfill you risk spillover while baking, so pour deliberately and check the edges.
Bake for 18 to 22 minutes: During this bake the filling will puff slightly, then settle into a glossy, set top with a gentle golden hue. You should listen for quiet bubbling at the edges and watch for the center to look set but still slightly jiggly, it will finish firming as it cools. The smell in the kitchen will be rich, sweet, and nut forward, signaling readiness. Avoid leaving it much longer than the top range which can dry the filling, or taking it out too soon which leads to a runny center.