Line a baking sheet with parchment paper and set aside.
In a medium saucepan over medium heat, melt the butter. Add the brown swerve sweetener and heavy cream, stirring constantly. Bring the mixture to a steady boil and let it cook for 3 to 4 minutes while stirring, until it darkens slightly and thickens to a syrupy consistency.
Remove the pan from the heat and quickly stir in the vanilla extract and sea salt. Add the pecan halves and sliced almonds, folding them into the caramel until every nut is evenly coated.
Pour the mixture onto the prepared parchment paper. Using the back of a greased spatula or spoon, spread it out as thin as possible into a single layer. Work quickly as the caramel will start to set.
Let the brittle cool completely at room temperature for about 30 to 40 minutes until it is fully hardened and snaps cleanly when broken.
Break the brittle into irregular shards and pieces. Store in an airtight container at room temperature for up to one week or in the refrigerator for up to 2 weeks.
