Preheat oven to 350 degrees F.
Put cupcake liners into 16 muffin tins.
In a medium bowl, whisk together flour, baking powder, baking soda, and salt. Set aside.
In another bowl, add eggs and beat on medium-high with an electric mixer for 20 seconds. Add sugar and beat on medium speed for another 30 seconds. Add vanilla and oil and beat on medium speed until combined.
With the mixer on low speed, add the flour mixture and the kefir and mix until combined.
Spoon batter into prepared muffin tins, filling until 1/2-2/3 full.
Bake for 12-14 minutes, until golden and a toothpick inserted into center comes out clean.
Let cool for a few minutes and then remove and transfer to a wire rack. Frost when completely cool.