Line an 8-inch square baking dish with parchment paper.
In a medium-sized saucepan, simmer the butter until it froths and brown flecks appear. Whisk in the erythritol, stevia, and vanilla and continue to heat for about 5 minutes, until well combined. Remove from the heat and allow to cool for 5 minutes. Pour into the prepared pan and place in the fridge to set, about 15 minutes.
Meanwhile, make the chocolate: In a small saucepan over medium heat, stir together the heavy cream, allulose, stevia, and vanilla. Bring to a light simmer. Place the chopped chocolate and scoop of Equip chocolate into a blender. With the blender running on low, slowly drizzle the hot cream mixture into the blender. Puree until the mixture is smooth and the chocolate is totally melted.
Remove the cooled toffee from the fridge. Drizzle the chocolate over the hardened toffee. Break into pieces for serving.
Store in an airtight container in the fridge for up to 2 weeks.