Students will find 3 recipes online, I recommend giving them one website to search through, I use allrecipes.com. There are thousands of options there for them to choose from. The recipes they choose must each contain a whole number, mixed number and fraction along with a minimum of 5 ingredients. They will record the the entire recipe, INCLUDING directions on the recording sheet. Then there is the sheet for work where they actually triple, double, or halve their recipes. After this they choose 1 recipe to make a final copy, including picture, and citation of where they got the recipe. I have my students make them on Google Docs, share it with me and then print copies of them all to create a class recipe book. You could also have them make a hard copy on computer paper if you would rather.
Then as the culminating activity, we have a buffet where the students can make the recipe they created for their final copy and the other students get to try new foods and go home with recipes of how to make them in their recipe cookbook.
This usually takes my 6th graders 4-5, 88 min blocks to complete. Rubric and example of final copy recipe is included.