Mix the butter, sugar and eggs until frothy. Stir in yogurt. Mix flour with baking powder and stir in. Stir in eggnog. Pour half of the batter into a springform pan. Spread the Duplo in pieces on top, pour the remaining batter on top and spread on it. Bake at 180 ° for approx. 70 minutes. If necessary, cover halfway through the baking time so that the cake does not get too dark.