Preheat oven to 350 degrees.
Whisk together the flour, baking powder, baking soda, and salt in a medium bowl. Set aside.
In a stand mixer fitted with the paddle attachment, beat the butter over medium speed. Add sweetened condensed milk and beat until fully combined and fluffy. Reduce mixer speed to low and slowly add the flour mixture, 1/2 cup at a time, stopping to scrape down the sides of the bowl if need be. Continue to mix until it is all incorporated and the dough is smooth, about 1 minute. Fold in the chocolate chips, peanut butter chips, and pretzel pieces by hand with a rubber spatula.
Line a baking sheet with parchment paper. Form 1-inch balls and place them at least 1-inch apart on the baking sheet. Bake for 10 to 12 minutes until the bottoms of the cookies are lightly browned. Remove from the oven and let cool.
For an extra treat, you may drizzle cajeta or dulce de leche on top.