Stir yeast with 1 teaspoon sugar until it becomes liquid. Knead flour, 50 g sugar, mixed yeast, 100 ml warm water and cream with the dough hooks of the mixer, kneading 40 g soft butter in flakes until the dough is smooth.
It forms a ball and separates from the bowl rim, continue kneading for about 3 minutes. Cover the dough and let it rise in a warm place for about 45 minutes until its volume has doubled.
Wash, halve and stone the plums. Halve the plum halves again lengthwise. Line a baking tray with baking paper and pour the yeast dough from the bowl directly onto the tray with slightly moistened hands.
With moistened fingertips, spread out from the centre outwards to form a large flat cake. Cover and leave to rise in a warm place for about 30 minutes.
Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Press the plum quarters into the dough from the centre in a circle almost vertically. Spread 20 g butter in mini flakes on the plums.
Bake in a hot oven for about 20 minutes.
Take out the dachi. Immediately sprinkle with 1 tablespoon of sugar and let it cool down.