Jammy Fruit Bars Recipe

Name: Jammy Fruit Bars Recipe
Ingredients: For the Dough:; 4 1/2 ounces old fashioned rolled oats, not quick cooking, instant, or thick cut (about 1 1/3 cup; 128g); 4 1/2 ounces all-purpose flour (about 1 cup, spooned; 128g); 6 ounces light brown sugar (about 3/4 cup, firmly packed; 170g); 1 teaspoon baking powder; 1 teaspoon (4g) Diamond Crystal kosher salt, plus more for sprinkling; for table salt, use about half as much by volume or the same weight, plus additional salt for sprinkling; 1/4 teaspoon baking soda; 1/4 teaspoon ground cinnamon; 6 ounces cold, unsalted butter, cut into 1/2-inch cubes (about 3/4 cup; 170g); 1 large egg, straight from the fridge (about 1 3/4 ounces; 50g); For the Filling:; 8 ounces jam (volume will vary; 225g) or 12 ounces juicy fruit, such as whole blueberries or raspberries, pitted cherries, sliced strawberries, or peeled and diced peaches (volume will vary; 340g); Lemon juice, to taste