Add the butter, Swerve, and heavy whipping cream to a saucepan over medium heat. As the butter melts, the mixture should become creamy and begin to bubble.

Bring the mixture to a gentle boil and whisk often as it cooks. The bubbles should look thicker and the coating should turn caramel-colored before you remove it from the heat.

Take the saucepan off the burner, then stir in the vanilla and pecan halves. The thick coating should cling to the nuts rather than run freely off them.

Divide the mixture into 12 even mounds on a parchment-lined baking sheet. Each mound should hold its shape as the coating begins to cool.

Let the pralines reach room temperature, then refrigerate them for 1 hour before serving. They should feel firm enough to lift from the parchment.