Pizzas always go down well here. I either use an Asda pizza base mix or make some dough in my breadmaker. Then give them some each to roll out & bowls of different toppings. They love eating what they've made themselves.
Ds (23 months) likes to make anything that involves using an electric mixer as he loves to hold it! Pavlovas are the current favourite (not that he's tasted the result, poor lamb!) because they involve lots of mixing.
Scones. Rubbing butter into flour is toddler heaven, as it being given a bit of dough to shape and play with.
Not being a big biscuit eater, it's not something I do often, but on a wet weekend a lot of entertainment can be got out of rolling biscuit dough, choosing and sometimes using biscuit cutters, then later on icing and decorating the finished product.
Eggy bread. Both mixing the egg and dipping the bread in the mixture are toddler jobs.
And finally...the staple of the sluglet's diet, cheesy potato. She holds the grater while I grate the cheese. I mash it together with a fork (while she eats bits of the grated cheese) and she 'finishes it off'. i.e. slaps the fork in the bowl a few times and announces it's OK now before shoving a great big lump of it in her mouth.