Preheat the oven to 375 degrees.
Combine and whisk the dry ingredients: 1 2/3 cup all purpose flour (213 grams), 1/4 teaspoon baking soda, 1 1/2 teaspoon baking powder and 1/2 teaspoon salt in a medium bowl until combined. Set aside.
Zest your lemons. Place the lemon zest and white sugar in a food processor and blend until the lemon zest is incorporated into the sugar. Set aside.
Make sure your wet ingredients are room temperature, set the 2 eggs and the extra creamy lemon skyr (125 grams) out on your counter to come to room temperature, while you juice the lemons. Measure out 1/4 cup whole milk (60 grams) and gently warm it until lukewarm.
Once the wet ingredients come to room temperature, combine the lemon sugar, 2 eggs, 1 teaspoon of vanilla extract, the container of extra creamy lemon skyr (125 grams), 1/4 cup of warm milk (60 grams), 1/4 cup lemon juice (60 grams) and 2/3 cup olive oil (150 grams) and whisk together until well combined. The mixture should be smooth and homogenous.
Note: Make sure everything is at room temperature, this way everything will combine smoothly together once whisked.
Using a rubber spatula, gently sift in the dry mixture into the wet mixture in batches. Fold the dry ingredients in until just combined. A few lumps are okay but do not over mix.
Line your tin with cupcake liners and fill each cupcake tin about 3/4 way. Bake the cupcakes on the top rack of your oven for 5 minutes at 375 degrees. Once the five minutes are up, reduce the temperature to 350 degrees and bake for another 10 minutes or until the centers of the cupcakes come clear when pricked with a toothpick. Pull the cupcakes out and let them cool for about 10 minutes in the pan. Remove the cupcakes from the pan and let them cool to room temperature. While the cupcakes cool, proceed to make the frosting.
Make the Lemon Skyr Frosting:
Beat softened butter using an electric blender until smooth and soft, about 2 - 3 minutes.
Add the extra creamy lemon skyr, lemon zest, vanilla extract and salt into the butter and beat until combined, about a minute or so.
Sift in the powdered sugar in batches until the frosting becomes thick and smooth. Scrape down the sides of the bowl periodically to make sure all the sugar gets incorporated.
Scoop the buttercream frosting into a piping bag fitted with your desired pipping tip.
Pipe the frosting onto the cooled cupcakes and top with a juicy lemon slice. Enjoy!