Half as many, much, etc. again
Definition 1 of 1
Pro Tip 1/3Quantitative Increase
Use when you mean something has increased by 50%. 
Last year we sold 200 units, but this year we sold half as many again.
Pro Tip 2/3Proportion Misunderstanding
Remember, it's not doubling the amount - it’s adding 50% more. 
Instead of 2 liters, he bought half as much again, so he got 3 liters.
Pro Tip 3/3Not Multiplicative
It's additive; you're putting 50% more on top of the original, not multiplying by 1.5. 
They didn't double the recipe; they just used half as much again of each ingredient.