One Bowl Blueberry or Cranberry Crumble Bars

I saw these online and had a real craving for them - I knew they would be similar to the datebars of my youth, but way easier. It's a quick recipe and perfect when blueberries are abundant.   In 2022 when we gathered in Chestertown for Thanksgiving, Zach and Becca brought several quarts of CSA cranberries that people had failed to pick up, or left behind. We experimented making Cranberry Crumble bars (fun to say!) and they were such a hit I made a second batch. Super easy, and so pretty.

You make the same dough for the bottom layer as the streusel topping - super easy. I cut the sugar, as my first version seemed sweeter than needed.

Crust and Crumble Topping
1/2 c (1 stick) butter, melted (microwave on low power, in a big bowl that you then use to mix the dough). For vegans, use parve margarine.
1 c flour (half WW, half regular, as I always do)
3/4 c old-fashioned whole-rolled oats
1/4 c granulated sugar
1/4 c light brown sugar, packed

salt to taste

Blueberry (or Cranberry) Layer
1 pint washed blueberries or 12 oz. cranberries (1 1/2 c)
1/3 c granulated sugar
For blueberries: 2 T lemon juice (1 lemon's worth) - omit for cranberries
2 t cornstarch

• Preheat oven to 350. 
• Line an 8 or 9-inch square pan with a parchment paper sling.
• Altrnatively, to make individual tarts (as I just did during COVID), spray a silicone muffin tin. I made 12. You could make 16, just use 2 trays and leave 8 empty. It's a little more work but a dozen big wows! Wait until cooled to remove, by popping them out from the bottom of the tray.
• In a large, microwave-safe bowl melt the butter.
• Add the flour, oats, sugars, optional salt, and stir to combine. Mixture will be dry and sandy with some larger, well-formed crumble pieces.
• Set aside 1 heaping cup mixture for the top crumble layer.
• Transfer remaining mixture to prepared pan, and using wet fingers, pack the mixture to create an even, smooth, flat crust; set aside.
• In the large mixing bowl (same one!), add blueberries, lemon juice (not for cranberries!), sugar, and cornstarch, stirring to combine. If sugar hasn’t dissolved fully that’s okay because it liquifies while baking.
• Evenly distribute blueberry mixture over the crust.
• Sprinkle with the reserved heaping 1 cup crumble topping mixture. squeezing the mixture to shape bigger crumble pieces.
• Bake for about 45 minutes (in the Breville), or until edges are set and center has just set. Crumble topping should appear set and very pale golden. 
• Place pan on a wire rack and allow bars to cool for at least 30 minutes before slicing and serving. If you try to slice bars before they’ve cooled completely, they’ll be extremely messy and could fall apart. 
• To cut when cooled, pull out with the sling onto a flat cutting board. Cut 4 x 5 or even 5 x 5 with a pizza cutting wheel or sharp, wet knife. These are messy-ish, so small bite-size bars are great.