Preheat the oven to 350 degrees.
Zest the lemons; set aside. Juice the lemons. You will need 1/2 cup of juice. Place the juice into a small saucepan and slowly bring to a boil. Reduce heat and simmer until the juice is reduced by half yielding 1/4 cup. Place the juice in a bowl and set aside to cool.
Cream together the avocado oil, sugar, and lemon zest in the bowl of a stand mixer fitted with a paddle attachment. Add in the eggs one at a time and mix until the mixture is smooth.
Add in the cream (or milk alternative) and lemon juice and mix.
Add in the gluten free flour, baking powder, and salt. Mix on low speed just until the dry ingredients are incorporated then turn the mixer off. Using a silicone spatula fold the ingredients together until a smooth batter forms (this should only take a few turns of the spatula).
Place the frozen wild blueberries into a small bowl and toss with one teaspoon of gluten free flour. Spoon the berries (leaving any loose flour behind) into the batter. Fold the berries into the batter gently and only a few times. Over mixing the berries will create a purple-tinted batter.
Liberally spray each muffin cavity with nonstick cooking spray.
Fill each muffin 3/4 full with the batter.
To create the crumb topping, cut one stick of butter into small cubes. Combine with 1 cup of gluten free flour and 1/2 cup of sugar. Using your hands work the ingredients together until combined and large crumbs form.
Evenly distribute the crumbs among the muffins being sure to cover the surface of each muffin. Very gently, lightly press the crumbs down so they are touching the batter (not not press too hard or you will submerge the crumbs).
Bake for 30-35 minutes or until the crumbs are golden and a cake tester inserted into the center of the muffins comes out clean.
Allow the muffins to rest in the tin for 5 minutes. Then, transfer the muffins to a cooling rack and allow them to completely cool for 1-2 hours.