Preheat your oven to 350°F (175°C).
In a clean, small bowl, use a hand mixer or a whisk to beat the egg white until stiff peaks form. This is the key to a light and airy muffin.
In a separate bowl, stir together the pumpkin seed flour, mayonnaise, melted coconut oil, sweetener, and baking powder until well combined.
Gently fold the pumpkin seed mixture into the whipped egg white, being careful not to deflate the air you incorporated.
Pour the batter into a single silicone baking cup or a greased ramekin.
Bake for 15 minutes, or until the muffin is golden and a toothpick inserted into the center comes out clean.
Serve immediately with a pat of room-temperature butter melting on top.
