A shortbread-style base supports cheesecake filling, blueberries and a buttery crumble in these chilled bars. Keep the crust, filling and topping ingredients in separate groups. Slice only after the center is cold and firm. Label the three bowls crust, filling and crumble before measuring: the two half-cup butter portions belong to the crust and topping, while the cream cheese belongs to the filling. Keep both butter portions cold until you cut them into their dry mixtures. The rolled oats are optional in the topping; they are not an ingredient to replace the crust flour. Wash and dry fresh berries so surface water does not collect on the filling. Spread the cheese mixture gently over the partially baked crust without dragging up crumbs. Leave the crumble loose rather than pressing it into a solid lid. Check the center filling as well as the browned topping, then chill thoroughly before lifting the slab. Use the parchment to support it and wipe the knife between cuts for cleaner edges.