Preheat oven to 350 F. Line a quarter sheet pan with parchment paper. Make sure the parchment comes up over the edges to make it easier to pull out the blondies after baking for clean slices.
Prepare the brown butter. Place the 2 sticks of salted butter in a small sauce pan over medium low heat. The butter will melt then start to foam. Turn down the heat to prevent burning the butter and watch for the milk particles to start to brown. I just like to swirl the butter every so often. You will know you are getting close to brown butter when the kitchen starts to smell lovely. This will take around 5 minutes depending on your stove and pan.
Set the brown butter aside to cool a bit. Mix the flour, oats, and baking powder together in the mixing bowl.
To the sauce pan of brown butter, add the brown sugar and whisk vigorously for 1 minute. Add in the 2 eggs and vanilla and whisk again for another minute. The mixture will be glossy.
Add the wet ingredients into the dry and mix to combine. Then fold in the chocolate chips reserving a small handful for topping the blondie batter once it is in the pan. Pour into the lined sheet tray, top with the remaining chocolate chips and bake on middle rack for 30 minutes.
Allow to cool in the pan for 10 minutes before using the parchment to pull the blondies out of the pan. Cool for another 10 minutes before slicing.
