Preheat the oven to 335°F / 170°C and line a muffin pan with cupcake liners. Make sure the butter, eggs, and milk are at room temperature before beginning.
Split the milk into two containers, one with ½ cup of milk (118g) and one with ¾ cup of milk (177g).
Mix the ½ cup of milk with the vegetable oil and set aside.
Mix the ¾ cup of milk with the eggs and vanilla. Whisk together lightly and set aside.
Place the flour, sugar, baking powder, and salt into the bowl of your mixer and turn on low with your paddle attachment.
Slowly add the butter, one small chunk at a time, letting it mix for a few seconds in between additions. Once it's all in it should look kind of like chunky breadcrumbs
Add the milk/oil mixture and turn your mixer up to medium speed. Beat for exactly two minutes.
Scrape the sides of your bowl to make sure there are no lumps, then turn the. mixer back on low.
Add the milk/egg mixture slowly and mix on low until just combined.
Divide the batter into 24 cupcake liners and bake for 18 minutes or until the tops are springy and a skewer comes out clean.
Let the cupcakes cool in the pan for 5-10 minutes before moving to a wire rack to cool completely.
Make the Russian Buttercream
Make sure the butter is completely at room temperature.
Put the butter in a stand mixer fitted with the whisk attachment and whip on high for 5 full minutes, scraping down the sides of the bowl occasionally.
Turn the mixer down to medium speed and slowly drizzle in ⅓ of the condensed milk and whip until totally incorporated.
Repeat until all the condensed milk is added.
Add vanilla and salt and then beat on high speed for 1 minute.
The buttercream should be thick and glossy. If it isn't, see the troubleshooting guide in my Russian Buttercream post. Once it's the right consistency, add the food coloring and whip until evenly distributed.
Pipe or spread the buttercream onto your cupcakes and decorate with heart sprinkles.
Notes
*Food Coloring - Make sure you use a gel food coloring. The liquid kind you can buy in the grocery store is usually not strong enough for use in baking and may mess with the consistency of your frosting. I used this one in my frosting. Buttercream - the Russian buttercream is just one of many frostings that pair well with these cupcakes. For more info on Russian buttercream, see this recipe post. Or for inspiration for other frostings to make with these cupcakes, see the 'Variations' section in the blog post above.