Preheat the oven to 350℉ (175℃) if not still preheated. Line an additional cookie sheet with parchment paper.
In a medium bowl, whisk together the flour, baking powder, baking soda and salt. Then set aside the flour mixture.
2 3/4 cups (344 g) all purpose flour, spooned and leveled , 1/2 tsp baking powder, 1/2 tsp baking soda, 1/2 tsp salt
In a large bowl cream the softened butter and granulated sugar together with an electric hand mixer on high speed until fluffy, about 2 minutes.(You can also use the bowl of a stand mixer fit with a paddle attachment.) 1 cup (200 g) granulated white sugar, 1 cup (227 g) unsalted butter, very softened
Add in the egg and vanilla and mix on medium speed until pale in color and very fluffy, about 1-2 minutes.
1 egg, at room temperature, 2 tsp vanilla
Add in the dry ingredients. Mix on low speed just until combined.
Add in the white chocolate, and fold it into the cookie dough with a rubber spatula.
6 oz (170 g) white chocolate bars, chopped
Push 3/4 of the dough to the side of the bowl. Flatten out 1/4 of the dough on the bottom of the bowl. Spoon 1/4 of the jam onto that section of dough. Add 1/4 of the dough on top of that section and spoon 1/4 of the jam on top. Repeat twice more. (Basically, we are trying to evenly disperse the jam!)
"Cut" the dough in quarters with a rubber spatula and fold each section of dough just until the jam is slightly folded in. Don't mix the jam in all the way, you'll want there to be little pockets of jam throughout the dough.
Scoop the dough into 22 portions with a 2 tbsp cookie scoop. (The scoop should be slightly overfilled.)
Place the cookie dough scoops at least 2 inches apart on the baking sheets. Press down lightly with your finger tips to slightly flatten each scoop. (See photo in the blog post above.)Bake 6 cookies at a time. Bake the cookies for 10-11 minutes. (When the cookies are straight out of the oven, scoot a large circular cookie cutter around them to give them a perfect circular shape.) Let the cookies cool for about 10 minutes on the cookie sheet, then transfer the baked cookies to a cooling rack to cool completely.