1 Heat up the oven to 375°F. Grease and flour a 9-inch springform cake or deep-dish pie pan.
2 First make the oat topping: Mix the flour, brown sugar, and spices in a medium bowl. Drizzle in the oil and crumble it around with your fingers so that you get little pea-size bits of oil all through.
3 Now for the cake batter: In a glass, add the lemon juice to the milk and set it aside for a few minutes.
4 In a large bowl, mix together the lemon zest, granulated sugar, oil, and vanilla. In a smaller bowl, whisk together the flours, baking powder, and salt.
5 Add the milk mixture to the bowl with the sugar and stir. Now, slowly stir the flour mixture into the bowl with all the wet stuff. Mix them all together until everything is well combined. The batter will be thick as hell, but you’re all good so keep going. Fold in 1.5 cup of the berries and stir a few times to make sure they are mixed in.
6 Now assemble. Pour the batter into the prepared pan and then throw the remaining berries on top. Gently press those berries into the batter a little bit so they aren’t loose. Just a gentle pat will be all good. Evenly sprinkle the oat topping over all of that and throw the pan in the oven on the middle rack. Bake until the topping appears golden and a toothpick stuck into the center comes out without a bunch of raw batter all desperate and clinging to it, 35 to 45 minutes.
7 Let the cake cool for at least 45 minutes to 1 hour in the pan before serving.
Oat flour might sound fancy, but it’s really not. Just measure out some rolled oats, throw them in a blender or food processor, and run it until it is flour.