Use the bottom of a measuring cup or glass to press the oat mixture firmly and evenly into the pan, creating a compact crust that won't crumble when serving.

Melt your unsalted butter until it turns golden brown before mixing with the crust ingredients to add a rich, nutty complexity that elevates the shortbread flavor.

Whisk the pumpkin pie spice with the pumpkin puree and sweetened condensed milk for 30 seconds before adding eggs—this blooms the spices and distributes flavors evenly throughout the filling.

Check bars for doneness at 20 minutes by inserting a toothpick near the center—it should come out with moist crumbs, not clean, as they'll continue cooking while cooling.

Cool bars completely at room temperature for 2 hours, then refrigerate for at least 4 hours before cutting—cold bars slice cleanly with crisp edges instead of crumbling.