Boil the potatoes in salted water until they are fork-tender (15-20 minutes).Remove from the heat and drain water.
Make batter
Pass the mashed potatoes through a potato ricer. There should be no lumps.Mix the mashed potatoes with eggs, milk, vanilla extract, baking soda, butter, sugar, and salt. Whisk until it is well mixed.
Bake
Place into self-standing paper cups or ramekins. Bake for 35 minutes or until they get golden brown on top.
Serving
Take out of the oven. They will quickly deflate (don't worry!). Fill the hollow space with the strawberry jam.Serve at room temperature.