Preheat the oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners. Preheating ensures consistent oven temperature so the cupcakes rise evenly and set properly.

Whisk the dry ingredients: in a medium bowl, sift or whisk together 1 1/2 cups (187.5 g) all-purpose flour, 1 1/2 teaspoons (6 g) baking powder, and 1/2 teaspoon (3 g) fine salt. Whisking distributes the baking powder and salt evenly and aerates the flour for a lighter crumb.

Cream butter and sugar: in a large bowl, beat 4 tablespoons (56 g) softened unsalted butter with 1 cup (200 g) granulated sugar until pale and slightly fluffy, about 2 minutes with a hand mixer or 3–4 minutes with a stand mixer on medium. Creaming incorporates tiny air bubbles that help lift the cupcakes and gives a finer texture.

Add oil and eggs: add 1/4 cup (60 ml) neutral oil and beat until combined (oil keeps the crumb moist and tender). Add the eggs one at a time, beating well after each addition so the batter emulsifies — this prevents splitting (curdling) and creates a uniform structure.

Add vanilla: stir in 2 teaspoons (10 ml) pure vanilla extract to flavor the batter consistently throughout.

Alternate flour and milk: with the mixer on low, add the dry ingredients in three additions, alternating with 3/4 cup (180 ml) whole milk (dry-wet-dry), beginning and ending with the dry. Mix only until just combined after each addition — overmixing develops gluten and yields tougher cupcakes. Scrape the bowl once between additions to ensure even mixing.

Portion the batter: using a 1/4-cup measure or a medium cookie scoop, fill the prepared liners about 2/3 full. This produces an even dome as the cupcakes rise without spilling over. Tapping the pan lightly on the counter evens the batter and releases any large air pockets.

Bake: bake at 350°F (175°C) for 16–18 minutes, rotating the pan halfway through for even browning. The cupcakes are done when the tops are springy and a toothpick inserted into the center comes out clean or with a few moist crumbs. Baking at this temperature creates a tender crumb while giving a gentle domed top.

Cool in pan briefly then transfer: let cupcakes cool in the tin for 5 minutes to set, then transfer to a wire rack to cool completely. Cooling in the pan too long traps steam and can make the bottoms soggy; immediate transfer prevents that and allows them to cool evenly.

Make the buttercream: beat 4 tablespoons (56 g) softened unsalted butter on medium speed until creamy, about 1 minute. Gradually add 1 1/2 cups (180 g) powdered sugar, beating on low to incorporate (to avoid a sugar cloud), then increase speed and add 1 tablespoon (15 ml) whole milk and 1 teaspoon (5 ml) vanilla extract. Beat until light and silky, about 1–2 minutes. Adding the liquid after the sugar helps you gauge the consistency and prevents a runny frosting.

Frost the cupcakes: once cupcakes are completely cool, pipe or spread the buttercream on each cupcake. Chill briefly (10–15 minutes) if you want the frosting to set for neater presentation. Chilling firms the buttercream and helps it hold shape if you're stacking or transporting.

Serve and store: serve at room temperature. Store cupcakes in an airtight container at room temperature up to 2 days, or refrigerate up to 4 days (bring to room temperature before serving). Buttercream chills firm but becomes silkier at room temperature.