1. 1. Prepare your baking dish: Preheat your oven to 375 F (190 C). Lightly grease an 8×8 inch baking dish with coconut oil or line it with parchment paper, leaving an overhang on the sides for easy removal. This step ensures your bars won’t stick and makes cleanup a breeze.

2. 2. Combine dry ingredients: In a medium mixing bowl, whisk together the rolled oats, almond flour, baking soda, and salt. Make sure there are no lumps and everything is evenly distributed. This creates the dry base for your bars.

3. 3. Mix wet ingredients: In a separate larger bowl, combine the active sourdough starter, maple syrup, melted coconut oil, and vanilla extract. Whisk until well combined and smooth. The sourdough starter should be bubbly and active for the best texture and flavor.

4. 4. Combine wet and dry mixtures: Pour the dry ingredient mixture into the wet ingredient mixture. Stir gently with a spoon or spatula until just combined. Be careful not to overmix; a few lumps are perfectly fine. The dough will be thick.

5. 5. Prepare the strawberry filling: In a small bowl, toss the diced fresh strawberries with the cornstarch or arrowroot powder. This coating will help thicken the strawberry juices as they bake, preventing a watery filling.

6. 6. Assemble the bars: Press about two-thirds of the dough mixture evenly into the bottom of your prepared baking dish. Spread the strawberry mixture over this base layer. Then, crumble the remaining one-third of the dough over the strawberries. Don’t worry about perfect coverage; a rustic, crumbly topping is part of the charm.

7. 7. Bake the bars: Place the baking dish in the preheated oven and bake for 25-30 minutes, or until the topping is golden brown and the strawberries are bubbly. The edges should look set, and a toothpick inserted into the oat base (avoiding the fruit) should come out mostly clean.

8. 8. Cool before slicing: Once baked, remove the dish from the oven and let the bars cool completely on a wire rack before slicing. This is a crucial step! Cooling allows the bars to firm up, making them much easier to cut into neat squares without crumbling.