Start by melting the butter. Set it aside while prepare the granulated sugar and lemon zest.
40 g butter
In a large mixing bowl add the granulated sugar and lemon zest. Rub it together to release all of the lemon zest flavor, until it looks like wet sand. Then add the melted butter and whisk together until combined.
100 g granulated sugar, 1 tablespoon lemon zest
Add the egg, sour cream, whole milk, vegetable oil, lemon juice, and vanilla extract and whisk it together until combined.
1 large egg, 45 g sour cream 14-18% or full-fat greek yogurt, 90 g whole milk, 2 tablespoon vegetable oil, 1 ½ teaspoon lemon juice, 1 teaspoon vanilla extract
In a separate bowl, sift the all-purpose flour, baking powder and salt. Add the poppy seeds and give it a stir to make sure everything has been combined. Add the dry ingredients to the batter and mix until combined.
160 g all-purpose flour, 1 ¼ teaspoon baking powder, ¼ teaspoon salt, 1 tablespoon poppy seeds
Using a rubber spatula, scrape down the sides of the bowl, and give the batter a final mix so everything has been incorporated.
Cover the bowl with some plastic wrap and let the batter rest for 1 hour on the kitchen counter.
While the batter rests, preheat the oven to 220ºC/425ºF conventional oven. Prepare a 12-cup cupcake pan with 6 cupcake liners, only lining every other cupcake hole, as it helps them to dome up. Grease around the edge of the cupcake holes, for the muffins to release easily.
Divide the cake batter into the 6 cupcake liners, so each cupcake holder is filled to the top. Be careful not to deflate the batter, so try not to mix it around it too much. Bake them for 7 minutes and then reduce the heat to 175ºC/350ºF and further bake them for 7-9 minutes or until cake tester comes out clean.
Let the muffins cool in the hot pan on a wire rack. After 5 minutes, remove the muffins from the pan and let them cool down additionally for 10-15 minutes before making the icing.