1. Preheat the oven to 180°C (350°F). Line a 23x23cm square baking pan* with baking parchment, grease lightly and set it aside.

2. Blend the rolled oats (100g/3.5 oz) in a food processor to get oat flour/finely ground oats. Add them together with the flour, sugar, and vanilla powder to a large bowl and mix to combine. Next, add the butter in small pieces as well as the egg, and mix everything until you get different-sized streusels – we normally do that by hand. Transfer about 2/3 of the streusels to the prepared baking pan and press them down to get an even layer. Bake in the preheated oven for about 15 minutes.

3. While the base is in the oven, wash, dry, and cut the strawberries into small pieces. Mix sugar and cornstarch, then add it to the strawberries along with the lemon zest, juice, and vanilla extract. Mix until well combined. Let the strawberries marinate for a few minutes.

4. Remove the pre-baked base from the oven and spread the marinated strawberries evenly on top. Mix the remaining streusels with the 3 tbsp. of rolled oats and sprinkle them all over the strawberries. Bake the crumble bars in the preheated oven for about 35-40 minutes. The strawberries should bubble here and there, and the streusels should have a golden brown color. Remove from the oven and cool down on a wire rack. When cooled, place in the fridge for at least 1 hour.

5. Remove the crumble bars from the baking pan by lifting them out with the baking parchment. Cut into nine bars/squares (or more, if you prefer them smaller). Dust with confectioners’ sugar to your liking before serving.