Preheat and prep: Heat your oven to 350°F (175°C). Line a 12-cup muffin pan with paper liners or lightly grease it.
Mix the dry ingredients: In a large bowl, whisk together 1 1/2 cups almond flour, 1/2 cup vanilla protein powder, 2 tablespoons coconut flour, 2 teaspoons baking powder, 1 teaspoon cinnamon, and 1/4 teaspoon salt until no lumps remain.
Whisk the wet ingredients: In a separate bowl, whisk 3 large eggs, 1/2 cup plain Greek yogurt, 1/3 cup unsweetened almond milk, 1/4 cup avocado oil, 2 teaspoons vanilla extract, and 1/3 to 1/2 cup low-carb sweetener (adjust to taste).
Combine: Pour the wet mixture into the dry ingredients.
Stir gently with a spatula until just combined. The batter will be thick and scoopable. If it’s too stiff, add 1–2 tablespoons more almond milk.
Fold in extras: Add 1/3 to 1/2 cup of your chosen mix-ins, if using.
Don’t overmix.
Portion the batter: Divide evenly among the muffin cups, filling about 3/4 full. Smooth the tops with a spoon if needed.
Bake: Bake for 16–20 minutes, or until the tops are set and a toothpick comes out mostly clean with a few moist crumbs.
Cool: Let the muffins rest in the pan for 5 minutes, then transfer to a cooling rack. They firm up as they cool.
Taste and adjust sweetness: Once cool enough to handle, taste one.
If you prefer sweeter, note it for your next batch or add a smear of sugar-free jam or peanut butter.