Preheat & Prep:

1. Start by preheating the oven to 350 degrees F.
2. Line an 8×8 square pan with parchment paper. (I recommend leaving parchment hanging over 2 of the sides of the pan so it’s easy to lift the cake out later.)

To Make The Streusel:

1. Start the streusel by combining melted butter, flour, brown sugar, cinnamon, and salt.
2. Mix lightly with a fork just until clusters form and there aren’t any super floury bits. (It’s ok for it to look a bit powdery, just no big clumps of flour!). Try not to over-mix the streusel into a paste–stop when the clusters form.
3. Set the streusel aside.

To Make The Blueberry Coffee Cake:

1. Cream The Butter & Sugar. In a large mixing bowl or stand mixer, cream the softened butter and sugar for 2 minutes, until light, fluffy and smooth.
2. Add Eggs One At A Time, mixing to incorporate each egg before adding the next one. Then, add the eggs one at a time, mixing each egg all the way in before adding the next egg.
3. Mix In The Vanilla. Stir in the vanilla and mix to combine.
4. Add The Dry Ingredients. Scrape down the sides of your bowl and add the gluten-free flour, baking powder, baking soda, and salt. Mix until just blended.
5. Mix In The Sour Cream. Now, add the sour cream and mix for 30-60 seconds, until the mixture is lighter in color, smooth, and velvety.
6. Fold In The Blueberries. Add your blueberries and use a spatula to gently fold them into the batter until they’re well distributed.
7. Layer The Cake & Streusel. Add half the coffee cake batter to your prepared pan and spread into an even layer with a spatula or offset spatula. Sprinkle with half of the streusel mixture. Add the remaining cake batter in dollops to cover the streusel (it’s easier to spread over the streusel when you dollop it around the cake rather than dumping it all in the center!). Gently spread the cake batter into and even layer to cover the streusel. Top with the remaining streusel. Your pan will be pretty full!
8. Bake The Coffee Cake. Place the baking dish in the oven and bake at 350 degrees F. for 50-60 minutes, or until a toothpick inserted in the center comes out clean. The center shouldn’t be overly wobbly and should spring back fairly quickly when you gently press it with your fingers (careful! It’s hot!)
9. Cool + Glaze (If You Want) + Slice. Place the blueberry coffee cake on a wire cooling rack to cool for 10 minutes. Lift the cake out of the pan to cool the rest of the way if desired (faster) or let the cake cool in the pan until totally cool. Drizzle with glaze if desired & cut into slices!

To Make The Optional Glaze:

1. In a liquid measuring cup or small bowl, combine melted butter, maple syrup, milk, vanilla, maple extract (if using), and 1/3 cup powdered sugar.
2. Whisk until totally smooth, adding more powdered sugar as necessary until it’s mostly opaque and drizzles easily off your fork or whisk. (If the glaze gets too thick, you can thin it with a little more milk.)
3. Drizzle over cooled coffee cake before serving.