Can you post the recipe please? I think this might be interesting for some people. This said. The point of fasting, in terms of food is indeed :
- exclusion of certain ingredients : animal, fish and anything deriving from them
- eating once a day after the 3rd hour (thing generally ignored by many people)
- no alcoholic beverage and oil (all oils), excepted on Saturday and Sunday
Following this rules, you will see that your cake and meatless sausages might be prohibited because they might contain oil (today they put oil in everything), which would leave you with bread, fruits, vegetables etc, something less tasty. Actually, some ingredients are prohibited because they are known for stimulating the passions, in particular meat. Regarding the look for substitutes,it seems to me in contradiction with the spirit of the fast that is about thinking less about food. Sometimes, there is such a quest for substitutes that one might think more about food that in normal time. Another point of the fasting is the idea of eating with moderation too, so that you are still a bit hungry after eating and not full.
Concerning your case, in theory, birthdays and namedays should not be celebrated during lenten periods. But I do no know what is implied by celebrating a birthday or a namesday because celebrating a birthday is typically for me something for children, when you are happy to grow; doing it as an adult seems strange to me and in some cultures that are not westernized, it is seen in fact as childish and no adult does it. I once talked with someone from Djibuti who to Europe firts, he is 25, and he was surprised to see grown-ups in Europe celebrating their birthdays.