Preheat the oven to 350°F. Prepare an 8" square pan with a parchment sling or reusable silicone liner, then lightly grease the sides of the pan. Alternatively, line a 9" cake pan with a round piece of parchment or round reusable liner and lightly grease the sides.

To make the crumbs: In a medium bowl, whisk together the flour, masa harina, sugars, and salt. Add the butter and vanilla; toss to combine. Using a bowl scraper, a fork, or your fingers, work in the butter until crumbs form and no dry spots remain. Set aside.

To make the cake: In a small bowl, combine the masa harina, water, and vanilla. Stir until smooth, then set aside to allow the masa harina to hydrate while you prepare the rest of the batter.

In a large bowl or bowl of a stand mixer, combine the flour, sugar, baking powder, salt, and baking soda. Add the butter and mix at low speed until the mixture looks sandy, about 1 to 2 minutes.

Beat in the eggs, then mix until no dry spots of flour remain. Stop the mixer and scrape the bowl and beater(s) as needed; the mixture will be thick.

Add the hydrated masa harina and yogurt or sour cream all at once before starting to mix. Continue to stir until the batter is smooth. Stop to scrape the bowl and then mix again at low speed for 1 minute.

Use a flexible spatula to gently fold in ¼ cup (37g) of the blueberries into the batter by hand.

Transfer the batter into the prepared pan and spread it evenly all the way to the edges.

Sprinkle the remaining ½ cup (74g) blueberries evenly over the top of the batter, followed by the crumbs. Gently press the crumbs to adhere.

Bake the blueberry coffee cake for 54 to 58 minutes, until it's set in the middle and the crumbs are golden brown.

Remove the blueberry coffee cake from the oven and allow it to cool in the pan for 30 minutes.

Remove the blueberry coffee cake from the pan. Finish by dusting with non-melting sugar or confectioners’ sugar, if desired.