Preheat the Oven: Preheat your oven to 350°F. Line a muffin tin with paper liners or grease it with butter.

In a large bowl, whisk together the gluten-free flour, baking powder, baking soda, salt, and cinnamon. In another bowl, mix the granulated sweetener, brown sweetener, melted butter, eggs, vanilla extract, and milk. Stir the wet and dry ingredients together until just combined, then fold in the diced apples.

In a small bowl, mix the flour, brown sweetener, and cinnamon. Add the softened butter and use a fork or your fingers to combine until the mixture forms small crumbs.

Divide the batter evenly among the muffin cups, filling each about 3/4 full. Sprinkle the crumb topping over each muffin.

Place in the oven and bake for 18-22 minutes, or until a toothpick inserted in the center comes out clean.

Let the muffins cool in the pan for a few minutes, then transfer them to a wire rack to cool completely.