For the Cupcakes:

1. Preheat and prep: Preheat your oven to 350°F (175°C). Line a standard 12-cup muffin tin with paper cupcake liners. This prevents sticking and makes for easy cleanup.
2. Mix dry ingredients: In a medium bowl, whisk together the flour, sugar, baking powder, and salt until well combined with no lumps. Whisking aerates the flour and ensures even distribution of the leavening agents.
3. Combine wet ingredients: In a large mixing bowl, using an electric mixer on medium speed, beat together the eggs, oil, milk, vanilla extract, and sour cream (if using) until smooth and well combined, about 1-2 minutes. The mixture should be pale and slightly frothy.
4. Add dry to wet: With the mixer on low speed, gradually add the dry ingredients to the wet ingredients. Mix until just combined—do not overmix. Stop mixing as soon as you can’t see any more dry flour streaks. A few small lumps are perfectly fine and will dissolve during baking.
5. Fill liners: Using an ice cream scoop or ¼ cup measure, divide the batter evenly among the 12 cupcake liners, filling each about ⅔ full (roughly 3 tablespoons of batter per cupcake). This ensures nice domed tops without overflow.
6. Bake: Bake for 18-20 minutes, or until the tops spring back when lightly touched and a toothpick inserted into the center comes out clean or with just a few moist crumbs (not wet batter). The tops should be just barely starting to turn golden.
7. Cool: Remove the muffin tin from the oven and let the cupcakes cool in the pan for 5 minutes. Then carefully transfer them to a wire cooling rack to cool completely before frosting, at least 30-45 minutes.

For the Vanilla Buttercream (Optional):

1. Beat butter: In a large bowl using an electric mixer, beat the softened butter on medium speed for 2-3 minutes until light, fluffy, and pale in color.
2. Add sugar: Gradually add the powdered sugar, about 1 cup at a time, beating on low speed after each addition to avoid a sugar cloud. Once all the sugar is incorporated, increase speed to medium and beat for 2 minutes.
3. Add flavorings: Add the vanilla extract, salt, and 3 tablespoons of cream. Beat on medium-high speed for 3-4 minutes until light and fluffy. If the frosting seems too thick to pipe or spread, add the remaining tablespoon of cream.
4. Frost: Frost the completely cooled cupcakes using a piping bag with your favorite tip, an offset spatula, or a simple butter knife.