In a bowl, combine the dry ingredients: flour (sifted, if lumpy), baking powder, and salt. Whisk together and set aside.
In a large bowl, combine the wet ingredients: oil, melted butter, granulated sugar, condensed milk, eggs, lemon zest, and vanilla extract. Whisk together until smooth.
Sift the dry ingredients over the wet mixture, then gently fold everything together with a spatula. Mix just until there are no dry spots, being careful not to overmix.
Stir 3 ounces of grated cheddar into the batter, saving 1 ounce for the topping. Mix just until the cheese is evenly distributed.
Let the batter rest for about 1 hour, or overnight in the fridge if you have time. This step is optional, but it helps improve the flavor and texture and gives the cupcakes a better rise when baked.
When you’re ready to bake, preheat the oven to 375°F (190°C). Line the muffin tin with liners or lightly grease the cups if not using liners.
Spoon the batter into the cupcake molds, filling them almost to the top, then sprinkle grated cheddar cheese on each one.
Bake at 375°F (190°C) for 5 minutes, then reduce the oven to 350°F (175°C) and bake for 15 minutes more, or until a toothpick comes out with a few crumbs.TIP: Starting at a higher temperature helps the cupcakes rise, then lowering the heat lets them bake through evenly without burning. Let the cupcakes cool in the pan for a few minutes, then move them to a rack or plate to cool completely.