Preheat the oven to 350℉. Grease a loaf pan and line the bottom with parchment paper.
In a large bowl, rub the zest of 1 lemon into the 1 cup granulated sugar, then whisk in the the ½ cup plain full-fat yogurt and 3 large eggs, stirring and whisking until well blended. Add the 1 ½ cups oat flour, ¼ cup almond flour, 2 teaspoons baking powder, and ¼ teaspoon fine sea salt, mixing just to combine. Add the ½ cup oil and stir well to incorporate. Fold in the 1 ½ cups blueberries. Keep stirring until it forms a smooth batter. Pour and scrape the batter into the prepared pan.
Rest the batter while the oven heats, then place in the oven and bake for 30-40 minutes until a toothpick inserted into the center comes out clean. Do not overbake.
Cool cake on a rack for about 20 minutes; then turn it out of the pan to cool completely.
When the cake is thoroughly cooled, whisk 1-2 tablespoons lemon juice into the 1 cup powdered sugar until a thick glaze forms. Spread it over the top of the cooled cake.
Notes
What type of yogurt? I use either whole-fat plain yogurt or plain Greek yogurt. You could also use low-fat yogurt, but I would not use non-fat because you'll lose the richness from the higher-fat yogurt.
Another oil. You can use your choice of oil in this cake. I use melted coconut oil or vegetable oil interchangeably, depending on what I have on hand. But you can use any neutral oil you like.
Add vanilla extract. Add 1 teaspoon of pure vanilla extract to the batter for extra depth of flavor.
Skip the glaze. If you want to streamline this recipe even more, omit the glaze, but make sure to add the citrus zest to the batter as detailed in the tip above. You can use the zest of 1 or 2 lemons, depending on how strong you want the flavor.
Make it a cake. I love baking this cake as a pretty layer cake! Double the recipe and bake it in two 2 9-inch cake rounds. You can fill and frost the cake with a simple, lightly sweetened whipped cream, or do a cream cheese or vanilla buttercream frosting.
Try another fruit. Use this base and add raspberries, chopped strawberries, or even pitted cherries in season!