Preheat oven to 375 degrees. Prepare a muffin or cupcake pan with paper or silicone liners. Set aside.
To a bowl, add the dry ingredients: flour, granular sweetener, baking powder and salt. Whisk together until combined.
In a larger separate bowl, add the wet ingredients; almond milk, egg, oil and vanilla. Whisk together until combined. Gradually add the dry ingredients to the wet ingredients, using a whisk to combine. Do your best to not overmix.
Using a rubber scraper, gently fold in the blueberries.
Using a small ladle or large spoon, spoon the batter into the prepared muffin tin, filling each muffin to approximately 3/4 full.
Streusel topping: in a bowl, combine the flour, brown sugar substitute and salt. Pour in the melted butter and mix together with a fork. Streusel mixture will be crumbly and gravel-like. Top the batter of each muffin with the streusel mixture.
Place pan in oven and bake muffins for 18-20 minutes. Test for doneness by inserting a toothpick into the center of a muffin. If it comes out clean and crumb-free the muffins are done.
Store any leftovers in an airtight container in the refrigerator. Muffins will keep for up to 7 days refrigerated.