Here, one shaggy dough does double the work: First, as a oatmeal-cookie like foundation. Second, as a streusely topping. Between is a gooey layer of jam. I prefer a dark-hued variety, like blackberry or blueberry or plum, for color contrast. —Emma Laperruque
Add 2 1/4 cups rolled oats to a food processor. Blend until a fine flour forms. Add the brown sugar and salt and pulse to combine. Scatter the butter evenly on top and pulse until a shaggy dough just starts to form. Add the remaining oats and pulse a couple times to incorporate.
Remove 1 1/4 (loosely packed!) cups of streusel. Spread out the clumps (clumps are good!) on a plate and stick in the freezer to firm.
Meanwhile, preheat the oven to 350° F. Arrange a baking rack in the bottom third of the oven. Line a 9- by 9-inch baking pan with parchment. The easiest way to do this is cut a roughly 12- by 12-inch square. Now cut slits inward from each corner—this will help the paper fold into place. Smear a bit of butter inside the pan. Place the parchment inside and smooth out with your hands.
Press the remaining oat streusel into the lined pan, forming an even layer. Spread the jam on top. Take the streusel from the freezer—it should be very firm—and sprinkle on top.
Bake—on a rack toward the bottom of the oven—for 50 minutes, rotating halfway through. Let cool for at least 30 minutes in the pan, then use the parchment to remove from the pan, and transfer to a rack to cool completely. Cut into 16 or 12 or 9 pieces, depending on how big or little you like your jam bars.
These freeze well. I like to wrap them individually and grab on my way out the door.
Emma is the food editor at Food52. Before this, she worked a lot of odd jobs, all at the same time. Think: stir-frying noodles "on the fly," baking dozens of pastries at 3 a.m., reviewing restaurants, and writing articles about everything from how to use leftover mashed potatoes to the history of pies in North Carolina. Now she lives in Maplewood, New Jersey with her husband and their cat, Butter. Stay tuned every Tuesday for Emma's cooking column, Big Little Recipes, all about big flavor and little ingredient lists. And see what she's up to on Instagram at @emmalaperruque.