Make the crust: in a large bowl, mix oats, flour, brown sugar, white sugar, cinnamon and salt. Add cold, cubed butter and mix with your hands until crumbly. Reserve two cups of the mixture in the fridge for a later use.
Press the remaining crust mixture into a baking pan (13*9 inch). Press firmly.
Bake the crust for 15 minutes, then set aside.
Make the filling: peel the apples, then thinly slice. Arrange apple slices in a row on the cooled crust.
Sprinkle the apples with flour, sugar and cinnamon. Then, crumble the reserved crust mixture.
Bake for 35 minutes, until the crust is golden brown and the apples are tender.
Allow to cool, then cut into bars.
Notes:
In the video you can see I’ve arranged apple slices in one row, but after trying it, I think it’s not enough, try layering two layers or more (5 apples should be enough).