Pizza-making combining two builder patterns (Bloch's and Go4)
I'm not familiar with the given pattern, but there are still a few things that should be pointed out.

The method Maker in Pizza should not start with an uppercase letter.

The fields in the Recipe constructor are useless, as an int is automatically given the value of 0 if no other value is assigned to it.

public Recipe() {
    baseSize = 0;
    a = 0;
    b = 0;
    c = 0;
}


should be

public Recipe() {}


The class Recipe has the following methods: changeA(), changeB() and changeC(). However, it also has prepare1(), prepare2() and prepare3().

Though it is a wild guess from my part, I assume that prepare1() is related to the field a, prepare2() is related to b and prepare3() is related to c. Why are the methods not named prepareA(), prepareB() and prepareC() instead?

Which brings me to my next point: 

Even if you are experimenting with a pattern, you should still take the time to use relevant method and field names.

Sure, you're learning on the moment, but tomorrow (or in the future), will you be able to make sense of the field names you used? Will you be able to remember what you learned if you base yourself on an unclear example?

Some good examples could have been:


changeToppings() and prepareToppings()
changeSauce() and prepareSauce()
changeCrust() and prepareCrust()


etc.

Obviously, I have no knowledge at all regarding cooking, but I am sure that a recipe with the fields baseSize, toppings, sauce and crust is much more descriptive than a recipe with baseSize, a, b and c.



The following is a tip, so take it or leave it.

When I experiment with patterns, I fully immerse myself in the example I create.

In your case, you decided to use pizzas. Commit to it - use fields like toppings, crust, sauce, cheese, etc. and methods like cook, cut, etc. If you're going to call your class Pizza, it has to be feel like a pizza -- and I've never seen a pizza made of a, b and c. If you really have no idea, then you could use toppingA, toppingB and toppingC, as long as it makes sense.

I don't know if this applies to everybody, but to me, I find it easier to learn/remember something new when I use full words rather than non-descriptive characters 

e.g.:

The likelihood of remembering 


  Oh yeah, that's right, the Pizza class had a topping, a crust and a sauce!


vs 


  Oh yeah, that's right, the Pizza class had an a, a b and a c!"