Prep your pan and oven: Preheat the oven to 350°F (175°C). Line a 12-cup muffin tin with liners or lightly grease with oil spray.
Mix the cream cheese filling: In a small bowl, beat the softened cream cheese with powdered sweetener and vanilla until smooth.
Add a splash of heavy cream if needed to make it spreadable. Set aside.
Combine the dry ingredients: In a large mixing bowl, whisk almond flour, cocoa powder, baking powder, baking soda, salt, espresso powder, and granular sweetener until no clumps remain.
Add the wet ingredients: Whisk in eggs, melted butter, almond milk, and vanilla until just combined. Do not overmix.
If using chocolate chips or nuts, fold them in gently.
Fill the muffin cups: Divide the batter evenly among the 12 cups, filling each about two-thirds full.
Add the cream cheese swirl: Spoon about a teaspoon of the cream cheese mixture on top of each muffin. Use a toothpick or skewer to gently swirl it into the batter, creating a marbled effect.
Bake: Place the pan on the center rack and bake for 18–22 minutes, or until the tops are set and a toothpick inserted into the chocolate portion comes out with a few moist crumbs.
Cool: Let the muffins cool in the pan for 10 minutes, then transfer to a wire rack to cool completely. The crumb sets as they cool, so resist cutting in too soon.
Taste and adjust sweetness: Keto sweeteners can taste different warm vs. cooled.
Sample once cool and dust with a little extra powdered sweetener if you prefer a sweeter finish.