1-Preheat oven to 350°F and line an: Preheat oven to 350°F and line an 8-inch square baking pan with parchment paper.
2-Make crust and crumble: Make crust and crumble: Whisk together flour, oats, baking soda, salt, and cinnamon in a medium bowl. Whisk together melted butter, brown sugar, granulated sugar, and vanilla in a large bowl until combined. Add dry ingredients and fold in until incorporated.
3-Set aside 3/4 cup (220 g) of: Set aside 3/4 cup (220 g) of dough for topping (chill until ready to use). Press remaining dough evenly into bottom of prepared baking pan.
4-Bake crust for 14 to 16 minutes,: Bake crust for 14 to 16 minutes, until lightly golden and set. Transfer to a wire rack and cool for 15 minutes.
5-Make filling: Make filling: Combine raspberries, sugar, salt, cornstarch, and lemon juice in a heavy saucepan over medium-high heat. Bring to a boil, pressing firmly on berries to release juices, about 3 to 4 minutes. Reduce heat to low and simmer for 1 to 2 minutes, until filling is thickened and coats the back of a spoon. Remove pan from the heat and cool filling for 10 minutes.
6-Spoon raspberry filling over cooled crust and: Spoon raspberry filling over cooled crust and crumble reserved dough over filling.
7-Bake bars for another 40 to 42: Bake bars for another 40 to 42 minutes, or until topping is golden and filling slightly bubbly. Cool completely in pan on a wire rack. Just before cutting, chill in the freezer for 15 minutes. Carefully lift parchment and place bars on a cutting board; cut into squares with a sharp knife.
8-Store crumb bars in an airtight container: Store crumb bars in an airtight container in the refrigerator up to 3 days. Bring to room temperature before serving.