Begin by preheating the oven to 350°F (175C/155C Fan) with a cookie sheet pan inside.
In a large mixing bowl, cream together the butter and sugar until light (about 2 minutes using a hand held electric beater).
1 cup unsalted butter, 1½ cup superfine granulated sugar
Add the eggs and vanilla, beating to combine.
2 large eggs, 1½ teaspoon vanilla extract
Sift the flour, baking soda, baking powder and salt into the mixing bowl.
2½ cups all purpose flour, ½ teaspoon baking powder, ½ teaspoon baking soda, ½ teaspoon salt
Stir together with a spatula until you have a thick sugar cookie dough.
Add the white chocolate chips and half of your sprinkles. Stir to distribute.
12 oz white chocolate chips, ½ cup sprinkles
Scoop the cookie dough into 10 large balls, placing these on a piece of parchment paper (see note). I do this using an OXO #40 scoop, which is about a 1½ tablespoon size. Each of my giant cookie dough balls is made up of 3 scoops, so about 4½ tablespoons (or just over a ¼ cup measure).
Using lightly dampened palms, pick up a cookie dough ball at a time and gently flatten. Top this with a full size peep and then envelop the Peep in the dough, leaving a hole at the top so that the Peep is peaking through. Dip the cookie in the remaining sprinkles to coat the dough at the edge around the hole. Repeat until you have stuffed each of your cookie dough balls.
10 Peeps, ½ cup sprinkles
Carefully remove your preheated cookie sheet and line with parchment paper. Place a couple of your cookies well spaced on the sheet and return to the oven to bake for 13 minutes, until the edges just start to go golden.
Remove from the oven and use a bowl or large round cookie cutter to scoot around the cookies to help make these more rounded (see note).
Allow the cookies to cool on the cookie sheet for a few minutes before carefully transferring to a wire rack.
Place the cookie sheet back in the oven to warm up for a couple of minutes and repeat the process until you are done with your dough (see note).