This recipe, published in the Telegraph less than two weeks ago is a good example of acting quickly. I didn't have raspberry or gooseberry jam, as recommended, but I did have a blueberry conserve with extra fruit, which I was sure would have a similar tartness.
I've made lots of oaty sandwich bars where the lower and upper layers of dough are made from the same basic mixture, but here each layer is quite different - it means a bit extra work, but it's well worth the effort. The base is a shortbread made with rye and wheat flour and dark brown sugar, and the crumble topping is made with mainly oats, plus small quantities of both flours and light brown sugar. I followed the instructions for a clumpy crumble and refrigerated the topping for a while. It then needed crumbling to the right consistency to sprinkle over the base and jammy layer.
This all worked very well to produce a delicious crumble bar - Hubs described it as a portable fruit crumble, which is his favourite hot dessert, so I think he liked it! The jam was very fruity and still quite runny even after baking - I thought it might set more solidly after 45 minutes in the oven, but it kept it's soft-set consistency. This lead to the bars being quite fragile, so I think that next time I will make them in a slightly smaller tin (20cm square instead of 23cm) so that a thicker base will make them a little sturdier and easier to handle. Otherwise, no complaints!