Heat the oven to 350°F (175°C). Grease a 13 x 9-inch baking pan or line it with parchment paper, leaving a little overhang if you want to lift the cooled bars out easily.

Beat the softened butter, packed light brown sugar, and granulated sugar until the mixture is light and creamy. This usually takes a few minutes and helps create a tender, cohesive bar.

Beat in the eggs one at a time, mixing well after each addition. Stir in the vanilla extract until evenly distributed.

In a separate bowl, whisk together the all-purpose flour, baking soda, and salt. Gradually add this dry mixture to the butter mixture, mixing only until no obvious streaks of flour remain.

Fold in the quick-cooking oats and white chocolate chips with a sturdy spatula. Keep mixing gentle and brief so the dough stays soft rather than becoming dense.

Press or spread the dough evenly into the prepared 13 x 9-inch pan. Smooth the surface, especially at the corners, so the bars bake at the same rate.

Bake for 20–25 minutes, until the edges are lightly golden and the center looks just set. Do not wait for the middle to become deeply brown because the bars continue to firm as they cool.

Cool the pan completely for at least 30 minutes before cutting. Use a sharp knife to slice the slab into approximately 24 bars, wiping the blade between cuts for tidy edges.