This is a rectangular offering table with a channel running around the perimeter of the top surface and a spout in the center of one of the long sides. The interior surface is very weathered, possibly originally in high relief of depictions of offerings.
From el-Kurru, Sudan, pyramid 6 A (tomb of queen Arty), debris. 1919: excavated by the Harvard University–Boston Museum of Fine Arts Expedition; assigned to the MFA in the division of finds by the government of Sudan.
Harvard University—Boston Museum of Fine Arts Expedition