Prep: Preheat oven to 350°F (175°C) with rack in center. Line baking sheets with parchment. Ensure butter and egg are room temperature. Warm raspberry preserves for 15-20 seconds, stir, and let cool slightly.
Mix dry: In a medium bowl, whisk together flour, baking soda, and salt for 30 seconds. Set aside.
Cream butter and sugar: In a large bowl, beat softened butter and sugar on medium-high for 2-3 minutes until light, fluffy, and pale.
Add wet ingredients: Add egg and vanilla. Mix until fully incorporated, scraping bowl as needed.
Combine dry ingredients: Reduce speed to low. Gradually add dry ingredients, mixing just until a soft dough forms and no flour remains. Do not overmix.
Fold in white chocolate: Gently fold white chocolate chips into dough until just distributed.
Portion: Scoop dough into 1.5-tablespoon balls (about 35g each). Place on prepared baking sheets, 2 inches apart.
Create wells: Use your thumb or a ½ teaspoon measure to make a deep, wide indentation in each dough ball. Do not press through to the bottom.
Fill with jam: Drop 1 level teaspoon of warmed raspberry preserves into each indentation.
Bake: Bake for 11-13 minutes, until edges are set and lightly golden. Jam will be bubbling.
Cool on sheet: Let cookies cool on baking sheet for 10 minutes. The jam will be extremely hot.
Transfer and serve: Carefully transfer to a wire rack to cool completely, or enjoy warm (carefully!).
