Grain free birthday cake

My sweet baby girl turned 1! I wanted her to have a birthday cake to smash, but she has not been able to process rice or oats yet. She does fine if I eat it (as I am still nursing her), but she can't process them on her own yet. Therefore, I went looking for a recipe I could use to make a cake she could actually eat on her birthday. I tried a couple different recipes ahead of time so I knew how they turned out and knew what they tasted like (since I taste all her food first because I want to know what she is eating). The first cake I tried was one made with coconut flour and I found the recipe here. I used regular milk and a few other substitutions. It turned out well, but had a strong coconut taste and my husband is not a fan of coconut. It also did not store for long on the counter and I felt I had to toss the cupcakes (I thought this would be an easier way to try than making a cake) after about 4 days.
The second recipe I tried was a diet soy flour cake recipe. This turned out well also and seemed to last on the counter longer. The only issue I had was it fell in the middle and seemed to shrink a lot compared to regular cakes. The taste was great and my husband actually liked it. This was what we ended up going with for the smash cake. Little miss did well, enjoyed the cake, and had no issues with her tummy.
While this worked out for us, I am hoping she is able to eat grains soon. We have enough allergies and such in the family I would hate to see her suffer from food issues as well.