Prep the pan and oven: Heat the oven to 350°F (175°C). Line a 12-cup muffin tin with liners or spray well.

Mix dry ingredients: In a large bowl, whisk 2 cups almond flour, 2 tablespoons coconut flour, 2 teaspoons baking powder, 1/2 cup granular sweetener, 1 teaspoon cinnamon, and 1/4 teaspoon salt until combined and lump-free.

Combine wet ingredients: In a separate bowl, whisk 2 large eggs, 1/3 cup melted butter (slightly cooled), 1/2 cup sour cream, 1/3 cup unsweetened almond milk, and 1 1/2 teaspoons vanilla.

Make the batter: Pour the wet ingredients into the dry and stir until just combined. The batter will be thick but spreadable. If it seems too stiff, add 1–2 teaspoons more almond milk.

Mix the cinnamon swirl: In a small bowl, combine 2 tablespoons granular sweetener and 1 1/2 teaspoons cinnamon. This will be sprinkled into the muffins.

Fill and swirl: Spoon about 1 tablespoon of batter into each muffin cup. Sprinkle a scant 1/2 teaspoon of the cinnamon mixture over each. Add another tablespoon of batter, then another light sprinkle. Use a toothpick to gently swirl the layers.

Make the streusel: In a bowl, combine 1/2 cup almond flour, 2 tablespoons granular sweetener, 1/2 teaspoon cinnamon, and a pinch of salt. Stir in 2 tablespoons melted butter until crumbly. Optional: mix in 2 tablespoons chopped nuts for crunch.

Top the muffins: Divide the streusel over the muffins, pressing lightly so it adheres.

Bake: Place the tin on the middle rack and bake 18–22 minutes, or until the tops are set and a toothpick comes out mostly clean with a few moist crumbs.

Cool: Let muffins cool in the pan for 10 minutes, then transfer to a rack to finish cooling. They firm up as they cool, so resist cutting in too early.

Optional finishing touch: Dust with a little keto-friendly powdered sweetener right before serving for that classic coffee cake look.