Grease a loaf pan with butter, line the bottom with a rectangle of parchment paper, and set it aside. Toss blackberries in 2 tablespoons of the rice or all purple flour to coat, and set them aside for later. Preheat the oven to 350 degrees Fahrenheit.

In a large bowl, mix together the rice flour/all-purpose flour, almond flour, sugar, pistachios, lemon zest, baking powder, cinnamon, baking soda, and salt until combined. Make a well in the middle and add the eggs, yogurt, olive oil, vanilla, and lemon juice, and whisk until combined, incorporating it into the dry ingredients around it until a smooth batter forms. Use a wooden spoon to gently fold in the blackberries.

Empty the batter into the loaf pan and bake on the lower third rack of the oven until deeply golden and a toothpick inserted into the center comes out clean (aside from blackberry goo). This will take about 35 to 45 minutes, take care to tent with tin foil at the 25-minute mark if it’s browning too quickly (this tends to happen with yogurt + olive oil-based cakes). Once done, remove from the oven and allow to cool for 20 minutes before inverting the cake onto a wire rack to cool completely.

Whisk together all of the ingredients except the chopped almonds. Drizzle the glaze onto the cooled cake, sprinkle with the chopped almonds, and serve. The cake will keep very well in an airtight container in the refrigerator for up to 1 week.