Step 1

Fill medium saucepan with 2 to 3 inches water. Place over high heat and bring water to boil, then reduce heat to low. Place large heat-safe bowl on top of saucepan to create double-boiler. Note: top of water should not touch bowl. Be sure to leave space between.

Step 2

Add egg yolks, Swerve, lemon juice, and lemon zest (if using) to bowl. Vigorously whisk without stopping until mixture has thickened, approximately 8 to 10 minutes.

Step 3

Carefully remove bowl from heat. Add 1 tablespoon butter to mixture and whisk thoroughly until butter has completely melted. Repeat with remaining 4 tablespoons butter, adding in 1 tablespoon increments and melting completely before adding next tablespoon.

Step 4

When all butter is fully incorporated, carefully transfer lemon curd mixture to jar or bowl. Cover with plastic wrap, gently pressing plastic wrap against top of lemon curd.

Step 5

Place covered lemon curd in refrigerator and chill at least 2 hours or until completely cooled. Serve chilled.