Preheat your oven to 350F and spray or lightly grease a 12-muffin baking pan.
In a large mixing bowl, whisk together the flour, cornmeal, baking powder and soda, and salt.
In another mixing bowl, stir together the vegan buttermilk, sugar, and melted butter (or oil and water). Stir these wet ingredients together, then add them to the dry ingredients. Fold everything together with a spatula until just evenly mixed (a few clumps are OK). Fill your muffin pan about 2/3 of the way with the batter. You'll need enough batter remaining to add a tablespoon on top of each muffin when you finish. Top each partially filled muffin container with a scant tablespoon of jam. Finally, top the jam with another tablespoon (or so) of batter. The muffin pan should be 3/4 full when you're done.
Bake the muffins for 22-24 minutes, or until light golden brown and with set tops. Transfer the muffins to a cooling rack and cool for at least 20 minutes before enjoying. Muffins can be stored in an airtight container in the fridge for up to 3 days, or they can be frozen for up to 6 weeks.