Even Julia Child, she who made it her mission in life to convince ordinary American home cooks that they too could produce classic French cuisine — even Julia conceded that pie crust is problematic. It's a delicate balance: flaky yet flavorful; tender yet sturdy enough to stand up to the filling. You could spend your life trying to make the perfect pie crust. Or you could go to 4 Seasons Bakery in St. Charles and leave it in the flour-covered hands of Agi and Aaron Groff. From their tiny storefront, which they opened two years ago, the Groffs have been producing some of the finest pastry in the area, using only natural ingredients. Their macaroons and Linzer torte are rightly lusted after. But it's their pie we swoon for. The crust has achieved the perfect medium. (We're told that the trick is adding some steam to the convection oven, a maneuver we are not prepared to try at home. Even if we had a convection oven.) The fillings, made from seasonal fruit, are good, too: sweet but not cloying. But it's the crust that gets us. Oh, pie! We love you so, even enough to cross the mighty Missouri.