01 - Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper, allowing some overhang for easy removal.
02 - In a large bowl, mix rolled oats, all-purpose flour, light brown sugar, baking soda, and salt until evenly distributed.
03 - In a separate bowl, whisk together melted butter, egg, and vanilla extract until smooth.
04 - Pour wet ingredients into the dry mixture and stir until fully incorporated, forming a thick batter.
05 - Press the oat mixture evenly into the prepared baking pan, smoothing the surface.
06 - Bake for 22 to 25 minutes until edges are golden and the center is set. Allow the bars to cool completely in the pan.
07 - Beat powdered sugar, softened butter, milk, vanilla extract, and salt together until smooth. Add additional milk as needed to reach a spreadable consistency.
08 - Spread frosting evenly over the cooled oat bars. Let sit for 15 to 20 minutes to set, then lift out of the pan using parchment overhang and cut into 16 bars.