Mix 145 g of sweetened soy milk with 1 tablespoon (15 g) of vinegar, apple vinegar or lemon juice until thickened.
(If you're using milk, mix 155 g of milk with 1 teaspoon (5g) of rice or apple vinegar or lemon juice.)
Mash up the steamed sweet potatoes well. Combine with the egg, prepared "buttermilk," sugar and salt, and mix until smooth.
Sift the floury ingredients. Cut it into the Step 3 mixture to combine. Don't overmix.
Line a 18 cm square pan with parchment paper, and pour in the batter.
Bake in a 170 °C oven for 40 to 45 minutes. Adjust the time depending on your oven.
If you add 40 g of sugar or sweetner the cornbread will be just slightly sweet. If you add 70 g it will be quite sweet. Adjust the amount to your liking.
If you include some condensed milk in the liquid mixture, the cornbread will have a crispy finish.