Heat oven to 350 °F / 175 °C. Grease two 8-inch round pans, line with parchment, and dust with flour.

Whisk flour, baking powder, and salt in a bowl.

In a stand mixer, cream butter and sugar until pale. Beat in the eggs one at a time, then the vanilla.

On low speed, add dry mix in three additions, alternating with milk. Stop as soon as the batter looks smooth.

Divide batter evenly between pans, smooth tops, tap once to settle, and bake 25-30 minutes.

Cool 10 minutes, then gently turn each cake from pan onto a rack. Cool completely.

Trim any domes for flat layers. Swipe a spoonful of frosting on the cake board, add the first layer, and spread jam or a thin layer of frosting. Top with the second layer, inverted for a perfectly flat surface. Chill 15 minutes.

Cover the entire cake in a whisper-thin coat of white icing to lock in crumbs. Refrigerate 10 minutes.

Apply the remaining white buttercream, smoothing with an offset spatula until the dome looks perfectly round—like a baseball. Chill another 10 minutes to set.

Fit a piping bag with a small round tip. Pipe two mirrored curved lines across the top, then add short diagonal stitches along each curve to recreate authentic red seams on the ball.

Rest the cake at cool room temp for 20 minutes so the frosting softens slightly. Cut clean wedges with a hot knife, wiping between cuts. Enjoy, and store leftovers covered in the fridge for up to 3 days.