Preheat the oven to 350 F. Grease & flour a 10 cup bundt pan.
In a bowl, whisk together the flour, cocoa, baking powder, and salt.
In a large bowl, beat together the eggs and sugar until light and fluffy – about a full 5 minutes.With the beaters on, gradually pour in the oil, allowing it to blend into the batter as you pour.
Add half of the flour mixture to the bowl, beating as you add it in slowly. Pour in the kefir and vanilla, then the rest of the flour mixture. Beat to combine and have a smooth batter. Fold in the crumbled halva.
Pour into the prepared bundt pan and bake until you can press it in the center and it bounces back, about 60 minutes. Let the cake cool in the pan for at least 10 minutes but up to 30. Place a plate on top and invert the pan and lift up the pan so the cake is on the plate. Allow to cool fully before making the glaze.
For the glaze: in a skillet add the butter and cook until you can see brown bits. Transfer to a bowl, scraping the pan to get all the brown bits. Once it’s cool, skim off the top milky bit and discard. In a bowl, combine the brown butter bits, the powdered sugar and vanilla and add as much heavy cream as you need to make a thick glaze. Spoon it over the cake and add more crumbled halva.