In a large bowl beat the sugar and eggs until the mix is light and fluffy, at least 3 minutes.
With the beater on, slowly pour in the olive oil and beat to combine.
Add the salt, vanilla and beat to just combine.
Add the flour, baking powder, cocoa and keffir and beat to just combine. Don’t overbeat.
Fold in the chocolate chips.
Optional, for higher domes: Cover the batter with plastic wrap and set in the fridge to chill for 2-4 hours.
Fill muffin liners until ¾ full.
Melt the hazelnut spread in the microwave and spoon half a teaspoon on each muffin in circles on the top of the batter, swirl it in.
Preheat oven to 375 F.
Bake for 20 minutes, until the tops spring back when pressed or a cake tester comes out clean.