Preheat your oven to 375°F (190°C). Grease a muffin tin or line with paper liners.
In a large bowl, whisk together the flour, sugar, baking powder, and salt.
In another bowl, mix together the milk, vegetable oil, eggs, and vanilla extract.
Pour the wet ingredients into the dry ingredients and stir until just combined.
Fill each muffin cup halfway with batter. Add a teaspoon of jam to the center of each muffin, then top with more batter until the cups are about ¾ full.
Bake for 20 minutes, or until a toothpick inserted into the center comes out clean.
Let the muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.