1/2 tsp baking powder 1/4 tsp fine sea salt 6.3 oz/180 g unsalted butter, at room temperature plus extra to grease the baking pan 1 cup plus 2/3 cup/325 g superfine sugar 3 large eggs, at room temperature 1/2 cup/120 g kefir, at room temperature 1 tsp vanilla extract 4 Tbsp/60 ml warm milk 3 Tbsp/15 g usweetened Dutch-processed cocoa powder 1/2 tsp instant coffee granules 1 tsp raspberry extract 1/2 tsp red beet food color extract or any type of red food coloring
