World Big Dosa​

CJam, 214 bytes

ri[48_24C.25]{[48ZX]f{:DW$@*\md_D{_@\%}h;:M/iDM/}3/_{W=5<}#:I=[(\'/*]{S+_0e=!*}/["cup"2$2a>'s*+"tbsp"_'b-]I=S}%4/"rice
ukda chawal
urad dal
poha
methi seeds
Salt to taste
Water as needed"N/.+N*N@)2/" waiter"1$1>'s*

Try it online in the CJam interpreter.

Javascript (ES6), 443 chars

This was very fun to golf, but the result is considerably longer than what I was expecting.

d=n=>(y=s=>n<s?' cup':' cups',z=s=>n/s|0,A=' 1/4',B=' 1/2',C=' 3/4',n+y(2)+` rice
${n+y(2)} ukda chawal
${(n%2<1?n/2:z(2)+B)+y(3)} urad dal
${((e=n%4)<1?n/4:z(4)+(e<2?A:e<3?B:C))+y(5)} poha
${(n%48<1?z(192)+((c=n/48%4)>2?C:c>1?B:c>0?A:'')+y(193):n%3<1?z(12)+((f=n/3%4)>2?C:f>1?B:f>0?A:'')+' tbsp':(z(4)+(e>2?C:e>1?B:e>0?A:''))+' tsp')} methi seeds
Salt to taste
Water as needed
${(b=Math.ceil(n/2))} waiter`+(b<2?'':'s')).replace(/\n0 /g,'\n')

Try it out:

d=n=>(y=s=>n<s?' cup':' cups',z=s=>n/s|0,A=' 1/4',B=' 1/2',C=' 3/4',n+y(2)+` rice
${n+y(2)} ukda chawal
${(n%2<1?n/2:z(2)+B)+y(3)} urad dal
${((e=n%4)<1?n/4:z(4)+(e<2?A:e<3?B:C))+y(5)} poha
${n%48<1?z(192)+((c=n/48%4)>2?C:c>1?B:c>0?A:'')+y(193):n%3<1?z(12)+((f=n/3%4)>2?C:f>1?B:f>0?A:'')+' tbsp':(z(4)+(e>2?C:e>1?B:e>0?A:'')+' tsp')} methi seeds
Salt to taste
Water as needed
${(b=Math.ceil(n/2))} waiter`+(b<2?'':'s')).replace(/\n0 /g,'\n')

W=function(){setTimeout(function(){
    (Q=document.getElementById("num").value)&&(document.getElementById("a").innerHTML =d(+Q).replace(/\n/g,'<br>'));
  }, 10);};
document.getElementById("num").addEventListener("keypress", function(){W();});
document.getElementById("num").addEventListener("click", function(){W();});

<form>How many recipes of dosa batter would you like?
  <input type="number" name="num" id="num" value="1" />
</form>
<p id="a">1 cup rice<br>
1 cup ukda chawal<br>
1/2 cup urad dal<br>
1/4 cup poha<br>
1/4 tsp methi seeds<br>
Salt to taste<br>
Water as needed<br>
1 waiter</p>

It accepts values up to and even including 2^32, or 4294967296. After that, the 'urad dal' overflows on odd numbers and becomes negative.

Basically, it calculates the correct amounts as it goes. Luckily, only the methi seeds need to have tsp/tbsp/cup measures; otherwise, this would have been a whole lot longer. (The methi seed line alone is 155 chars!)

This also would have been at least 500 chars long in ES5. I ❤ ES6.

As always, suggestions are greatly appreciated!

Edit 1: Just realized that according to the rules, 1 tsp should be replaced with 1/3 tbsp, same with 2 tsp and 2/3 tbsp, as well as 16 tsp and 1/3 cup....

R, 602 603 526 bytes

Still lots of room to golf this I suspect, but I have run out of time and I really wanted to do an answer for this one.

function(i){S=gsub
M=i/c(1,5,60)
A=list(c(2,1),c(4,3),c(64,48))[[I<-max(which(M>=1))]]
B=c(4,12,192)[I]
V=c(' tsp',' tbsp',' cup')[I]
C=i%/%B
C=C+max((i%%B)%/%A*c(.3,.25))
cat(S('([ ]*)0 ','\\1',S('\\.3',' 1/3',S('\\.6',' 2/3',S('\\.5',' 1/2',S('\\.25',' 1/4',S('\\.75',' 3/4',paste0(i,' cup',if(i>1)'s',' rice
',i,' cup',if(i>1)'s',' ukda chawal
',i*.5,' cup',if(i>2)'s',' urad dal
',i*.25,' cup',if(i>4)'s',' poha
',C,V,if(C>1&I>2)'s',' methi seeds
Salt to taste
Water as needed
',ceiling(i*.5),' waiter',if(i>2)'s'))))))))}