This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
麨 combines 麥 (wheat) with 少, but the exact historical development is uncertain. It may have originally referred to a wheat product, but no clear meaning survives in modern Japanese.
The left side is wheat 麥, and the right side is few/little 少. Imagine a small amount of roasted wheat flour, which matches the kun-reading むぎこがし (roasted wheat flour).
For ショウ, picture a small show of wheat being roasted: show -> ショウ, and the wheat 麥 is being prepared in small 少 batches.