Preheat the oven to 350 degrees F. Butter an 8-inch square pan.
To prepare the filling: In a heavy-bottomed saucepan, combine the berries, sugar, flour, lemon juice, lemon zest, and water. Stir over medium heat until the mixture begins to simmer. Continue stirring until the berries just begin to break down and the sauce thickens, 3 to 4 minutes. Remove from the heat. To prepare the crust: In the bowl of a food processor fitted with the metal blade, pulse together the rolled oats, rye flakes, almonds, and sesame seeds just until they form a chunky, mealy texture, about 30 seconds. Add the flour, brown sugar, cinnamon, salt, and baking powder and pulse a time or two to combine. Add the egg and butter and pulse until the mixture has the consistency of large crumbs. Add the ice water slowly and pulse until the mixture just begins to clump together.
To assemble and bake the bars: Press approximately half of the crust mixture evenly into the bottom of the prepared baking pan. Pour the berry filling onto the crust and spread evenly. Scatter the remaining crust mixture across the top as you would for a fruit crisp or crumble--messy and haphazard, but evenly dispersed. Don't worry about pressing down; it will bake into the bars beautifully.
Bake until the top crumble is golden brown, about 30 minutes. Let cool completely in the pan. Slice into bars. If wrapped and kept at room temperature, the bars will keep for 3 days.
Make It Your Own: Try these with your favorite seasonal berries. Blackberries or huckleberries would be lovely, as would cherries.
"Whole-Grain Mornings: New Breakfast Recipes to Span the Seasons" by Megan Gordon. Copyright Ten Speed Press 2013. Provided courtesy of Megan Gordon. All rights reserved.