In a medium to large mug, add 1 tbsp butter and place in the microwave for 15-20 seconds or until the butter is melted.
Add allulose and stir well. Then add egg yolk and vanilla and whisk with a fork until well combined.
Add almond flour, salt, baking powder and sugar free chocolate chips, then stir until well combined. Then smooth the top with a spoon.
Place the mug in the microwave and cook for 45-60 seconds. Each microwave will require different cooking time. When a fork inserted comes out clean, your mug cake is ready to enjoy!