Daniel likes to make desserts for bake sales. Last month, he made 2 batches of brownies and 2 batches of cookies, which called for 12 eggs total. The month before, he baked 3 batches of brownies and 1 batch of cookies, which required a total of 12 eggs. How many eggs did Daniel use for a batch of each dessert?
Let B be the number of eggs per batch of brownies and C be the number of eggs per batch of cookies.
The total number of batches of brownies and cookies last month was 3 + 1 = <<3+1=4>>4.
The total number of batches of brownies and cookies last month was 2 + 2 = <<2+2=4>>4.
The total number of eggs used last month was 4B + 4C = 12.
The total number of eggs used last month was 3B + C = 12.
The total number of brownies used last month was 4B = 12.
The total number of cookies used last month was 4C = 12.
The number of eggs per batch of brownies is B = 12/4 = <<12/4=3>>3 eggs.
The number of eggs per batch of cookies is C = 12/4 = <<12/4=3>>3 eggs. Answer: \boxed{3}.