Step 1

Preheat the oven to 350°F. Grease a 9×2” cake pan and line it with parchment paper. Prepare the zucchini by placing the shredded zucchini in the center of a kitchen towel. Wrap up the towel and wring out most of the liquid by squeezing it over the sink. Set aside.

Step 2

For the streusel, combine the brown sugar and salt in a mixing bowl. Pour in the melted butter and use a fork to mix. Lastly, add in the flour and mix with the fork until just combined (it should be thick and crumbly). Set the bowl of streusel in the fridge.

Step 3

For the cake batter, combine the flour, baking soda, baking powder, and salt in a mixing bowl. Whisk to combine.

Step 4

Add the softened butter and sugar to the bowl of a stand mixer fitted with a paddle attachment. Cream together until light and fluffy, about 3 minutes. Mix in the vanilla. Add the egg and continue to mix until incorporated, scraping down the sides of the bowl as needed. Lastly, mix in the sour cream.

Step 5

Add the dry ingredients and mix on low until just incorporated. Fold in the zucchini and ¾ of the blackberries using a rubber spatula. Spread the batter into the cake pan. Top the cake with the streusel and remaining blackberries.

Step 6

Bake on the middle rack, uncovered, for 35 minutes. Cover the pan with a piece of aluminum foil. Continue to bake for about 8 more minutes, or until just cooked through. Remove the pan from the oven and let cool for about 20 minutes.

Step 7

Meanwhile, for the honey glaze, combine the powdered sugar, honey, and water in a mixing bowl. Whisk to combine.

Step 8

Use the parchment paper to gently lift the cake out of the pan and set it on a cooling rack. Drizzle the honey glaze over top. Sprinkle a pinch of flaky sea salt. Serve the cake warm or at room temperature, using a serrated knife to cut it into slices.