Ann's Lunar Rhubarb Cake - Test 1

Ann McMullen made us this cake, and it was delicious. She pointed out that she couldn't get the wood stove oven hot enough for the recommended temperature, which means we haven't experienced the cratered topping. I suspect I would like to add a bit more rhubarb to it. Oh, and I've start to beef up the instructions.

1 - My current oven seems to be cooler, which means everything takes longer to cook. It would be useful to gage the temperature, for which I need an oven thermometer. All that to say that in a rush, I put in this cake for the prescribed amount of time and I think the center was not quite cooked. Therefore I will leave this in the Testing phase. Also, I used the leftover rhubarb from making liqueur, so it had an extra kick!

2 - It is a very good cake, the crumb moist and tender with very little bite. I am using a different oven and I find it needs a bit more time, again. I also tried to quantify in terms of weight what 2 cups of rhubarb is, and I can't remember what I found. I think it was 300gr. And I found that wasn't quite enough. So whatever the amount was, 100 grams more of that, to try for next time!

3 - I think this was just right.

1/2 cup butter (4oz/114gr)
1/2 cup sugar (3.55oz/100g)
1 egg
1 tsp vanilla
1 cup buttermilk or sour milk
2 cups flour (reserve 2 Tbsps to mix with rhubarb)
1/2 tsp baking soda
1/2 tsp salt
2 cups (400g) rhubarb, diced
1/4 cup butter
2 tsp cinnamon
1 cup (7.1oz/200g) brown sugar 

1. Preheat the oven to 375F.
2. Cream together the butter and sugar until light; whisk in the egg and vanilla until smooth. Combine with the buttermilk/milk (this may look a bit lumpy as the fats won't mix easily with the liquid, but don't worry).
3. In a separate bowl mix together the flour, soda and salt.
4. In yet another bowl, combine the rhubarb with the reserved flour (or do this step using the butter bowl after you've emptied it).
5. Without overworking the dough, fold in the wet mixture into the dry.
6. Gently fold in the floured rhubarb.
7. Grease a 9x9 baking dish. Pour the dough into the dish, smoothing it evenly.
8. In a small bowl use a fork to combine the butter with the sugar and cinnamon until uniform and crumbly.
9. Sprinkle this crumbly mixture on top.
10. Bake in the oven for 40 minutes.