Classic Birthday Cake Recipe

Preheat the oven to 350F/177C and grease and line three 6 inch cake pans.
In a medium bowl, whisk together the flour, baking powder and salt until they're evenly distributed.
270 grams all-purpose flour spooned and leveled, 1 Tbsp baking powder, 1/2 tsp salt
Place the room temperature butter, oil and granulated sugar in a large bowl and use an electric mixer with the whisk attachment to beat them for 2 minutes.
56 grams unsalted butter room temperature, 120 mL canola oil, 300 grams granulated sugar
Add the eggs, one at a time, beating on medium speed until each egg is fully incorporated. Add the sour cream and vanilla extract and beat just until combined.
3 large eggs room temperature, 170 grams sour cream room temperature, 1 Tbsp vanilla extract
Add half of the dry ingredients to the wet ingredients, turn the mixer on low speed and then pour in the milk, followed by the rest of the dry ingredients.
180 mL milk room temperature
Distribute the batter evenly among the three cake pans, about 14oz in each pan and bake for 30-35 minutes. When the cake is fully baked it will release itself from the edge of the pan and it will spring back if you press on the center of it.
Invert the cakes onto a tea towel or cooling rack and allow the cake to cool completely before frosting.

For the frosting, melt the chocolate chips until they're smooth and silky. I do this in the microwave on 20-30 second intervals, stirring between each interval. You can also do it over a double boiler but make sure to stir the chocolate frequently.
255 grams milk chocolate chips
Once the chocolate is melted, remove it from the heat and continue to stir it every few minutes so it cools but doesn't harden.
Meanwhile, place the butter in a large bowl and use an electric mixer to beat it at full speed for about 5 minutes, until it's pale and fluffy. Make sure to scrape the edge of the bowl every couple minutes.
340 grams unsalted butter room temperature
Once the chocolate is no longer warm but still soft, pour it over the butter and beat the mixture until it's fully combined.

Place the first layer of cake on a flat surface and use 1/4 of the chocolate buttercream to frost it. Repeat with the second layer and then place the third layer on top.
Refrigerate the cake for 20 minutes and then use the rest of the buttercream to frost the outside of the cake. Top with sprinkles!
Sprinkles

Refrigerate the cake for another 15-20 minutes, just to set it, and then serve fresh. This Classic Birthday Cake is best served at room temperature within the first 1-3 days. Store fully covered, at room temperature for up to 48 hours and then refrigerated.

You can bake these cakes up in advance. To best preserve the moisture, allow the cakes to cool almost to room temperature, they should still be slightly warm. Wrap them in plastic wrap, place them in a freezer bag, pressing all the air out and freeze. Remove them from the freezer when you're ready to frost, this makes it easier to frost and they will defrost by the time you're ready to serve.
Optional: add 1/4 cup of cocoa powder to the buttercream to make it a darker chocolate or use dark chocolate chips instead of milk chocolate.