Unknown plant, please help me identify it
It appears to be a cultivar of Jujube (Ziziphus zizyphus) also known as Chinese date - https://en.wikipedia.org/wiki/Jujube
This is based on JimN's correct observation. I looked at a few dozen images of Ziziphus Zizyphus - both fruit and leaves. They appear to be identical. The fruit tastes as described. The fruiting progression matches the description in Wikipedia.