It means spending without measure. Act as a spendthrift. Waste, squander, waste, waste.
Deformation of the old verb malrotar (breaking bad, ruin), also pronounced as manrotar (if break with hands?, of spendthrift).
My grandmother and mother used this word in Coca, in the province of Segovia in the mid-20th century, when they referred to a meal that is marred by its poor confession or bad ingredients.
MARROTAR: Salamanca, destroy, spoil something.