Gradually add flour and powder. Continue to beat with a mixer.
Then add milk to the dough. Mix thoroughly (with a mixer at low speed). Place a glass of water in the microwave and turn it on for 30-60 seconds. Then remove the glass, close the oven.
Grease the mold with oil. Put the dough in a mold and flatten. Place the dish in the microwave and cover with a domed lid (there are special covers to protect it from splashing). Cook butter sponge cake in the microwave at 600 watts for 6-6.5 minutes. After turning off the microwave, do not open it for another 20-30 minutes.
Remove the finished biscuit from the mold. Trim the sides if necessary.