Preheat your oven to 350°F (175°C). Line a muffin tin with paper liners or lightly grease the cups.
In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, baking soda, and salt.
In a separate bowl, combine the unsweetened applesauce, melted butter, almond milk, vanilla extract, and egg. Whisk until well combined.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix, as it can lead to dense muffins.
In a small bowl, prepare the streusel topping by combining the flour, brown sugar, granulated sugar, and cinnamon. Add the cubed butter and use your fingers or a fork to mix until the mixture resembles coarse crumbs.
Fill each muffin cup with batter, filling them about 2/3 full. Sprinkle the streusel topping evenly over each muffin.
Bake in the preheated oven for 18-20 minutes or until a toothpick inserted into the center of a muffin comes out clean.
Once baked, remove the muffins from the oven and let them cool in the pan for about 5 minutes. Then transfer them to a wire rack to cool completely.