For the Raspberry Swirl:
In a small saucepan, gently combine raspberries, sweetener, and water. Cook over medium-low heat until it simmers and the berries soften enough to mash easily with a fork, about 5 minutes.
Sprinkle gelatin over the mixture and whisk quickly until fully dissolved. Set aside to cool.
For the Muffins:
Preheat your oven to 325°F (160°C). Line a 12-cup muffin tin with silicone or parchment liners.
In a large, microwave-safe bowl, melt the peanut butter and butter together. Microwave in 30-second bursts, stirring until smooth, or melt over a pan of gently simmering water.
Whisk in the brown sugar replacement until well blended. Then, add the eggs and vanilla extract, whisking until the mixture is smooth.
Add the almond flour, protein powder, baking powder, and salt to the wet ingredients. Stir well until combined; the batter will be quite thick. Gradually add the almond milk, a little at a time, until the batter thins to a spreadable consistency.
Spoon about half of the muffin batter into the prepared muffin cups. Add about 1 teaspoon of the cooled raspberry swirl to each cup and gently swirl with a knife.
Top with the remaining batter, then add another dollop of raspberry swirl to each muffin and swirl again with a knife for a beautiful pattern.
Bake for 20-25 minutes, or until the muffins are golden brown and firm to the touch. Let them cool in the pan before enjoying.