Heat oven to 350°F. Place paper baking cups into 24 muffin pan cups; set aside.
Combine cake mix, buttermilk, 1/2 cup lemon curd, oil and eggs in bowl. Beat at medium speed until well mixed. Stir in chopped thyme.
Divide batter among muffin pan cups. Bake 18-22 minutes or until toothpick inserted in center comes out clean. Cool completely.
Combine half & half and flour in 1-quart heavy saucepan; whisk until smooth. Cook over medium heat, whisking constantly, 3-4 minutes or until mixture thickens and just comes to a boil. Remove from heat; cool 15 minutes.
Combine butter and sugar in bowl; beat at medium speed until creamy. Add flour mixture; beat 5 minutes or until light and creamy and all sugar is dissolved. Add remaining lemon curd; beat until well mixed.
Frost or pipe frosting onto cupcakes. Refrigerate until serving time or up to 2 days. Decorate as desired before serving.
*Substitute 1 tablespoon lemon juice or vinegar and enough milk to equal 1 cup; let stand 5 minutes.
**Substitute fresh lemon thyme leaves.