Preheat oven to 350 degrees. Line standard muffin tins with paper liners. Cream butter, sugar, vanilla seeds, and orange zest until pale and fluffy. With mixer running, add eggs, 1 at a time, beating well after each addition and scraping down sides of bowl.
Combine cream, orange juice, and vanilla extract in a small bowl. Sift together
flour, baking soda, baking powder, and salt. With mixer on low speed, add
flour mixture to butter mixture in 3 batches, alternating with cream mixture, ending with flour; beat until just combined.
Divide batter among muffin cups, filling each 3/4 full. Bake, rotating tins halfway through, until testers inserted in the centers come out clean, about 25 minutes. Let cool in tins on wire racks. Undecorated cupcakes will keep, covered, for up to 1 day (or frozen for up to 2 months).
Using a serrated knife, trim tops of each cupcake to make level. Using an offset spatula, frost tops of each cupcake with some buttercream. Place a candied citrus slice on each cupcake. Fit a pastry bag with a small plain tip, and fill with remaining buttercream. Pipe dots around edges of orange slices. Cupcakes will keep, covered and refrigerated, for up to 1 day. Bring to room temperature before serving.