Preheat oven to 350 degrees F.
Line muffin tin with liners.
In large bowl add in the flour, baking powder and salt, mix to combine.
Cream the butter.
Add in the sugar, mix until light and fluffy.
Add in one egg at a time, mix completely.
Add in the flour mixture and buttermilk alternating each.
Add in the vanilla and vanilla seeds.
Mix completely to combine.
Pour batter into muffin cups.
Bake 25-30 minutes, or until toothpick inserted comes out clean.
Remove from oven, let cool completely.
In medium sauce pan add the egg whites and sugar.
On medium heat you are going to whisk egg mixture until sugar is completely dissolved (you can test it by rubbing a small amount between your fingers to test it, it should be completely smooth).
Remove from heat and let mixture cool. (If mixture is too warm it will melt your butter when the time comes).
Transfer to mixing bowl and with whisk attachment whisk on high until stiff peaks form and mixture is completely cooled.
Switch to paddle attachment.
On low speed add the butter one piece at a time.
Increase mixer to medium/high speed and mix until buttercream forms.
Add in the vanilla, continue mixing until completely mixed in.
When cupcakes are cooled pipe frosting onto each cupcake and sprinkle with sprinkles.
I used Wilton tips: 1M and 2D