Preheat oven to 350°F. Grease and line a 9-inch square pan with parchment, leaving an overhang.
Whisk flour, baking powder, and salt in a small bowl. In a large bowl, beat butter and both sugars until fluffy, about 2 minutes. Mix in vanilla, peppermint extract, and eggs one at a time.
Add dry ingredients, mixing just until combined. Tint with green food coloring until you get that Grinchy shade. Fold in crushed peppermint, white chocolate chips, and sprinkles.
Spread batter evenly in the pan. Top with heart sprinkles and extra festive bits. Bake 26–28 minutes, until edges are golden and the center looks set.
Cool completely in the pan, then chill for 1 hour for fudgier bars. Slice into squares and serve at room temp.