Place butter, sugar, and salt in a large bowl. Using a stand-up mixer with a paddle attachment or a handheld mixer, cream ingredients together at medium speed until light and fluffy (about 4 minutes).
Scrape down sides, add egg and vanilla, Beat for another 2-3 minutes, scraping down sides as necessary, until well combined. Add 3-4 drops of green food coloring and mix for another minute or until the green coloring is evenly distributed throughout dough and there are no streaks of color.
Slowly add flour, ½ cup at a time, mixing well after each addition. Dough should be firm, not sticky, but still be soft. Divide dough in half and put each half between two pieces of heavy-duty freezer plastic wrap or parchment paper. Roll each piece of dough to ¼" thick and place in refrigerator on flat surface for at least 30 minutes.
Preheat oven to 350F/176C degrees. Line baking sheets with parchment paper or use a silicone baking mat.
Remove one prepared dough sheet at a time from refrigerator. Remove top layer of parchment paper or plastic wrap and cut out 30 cookies using a round shaped cutter with a heart insert. Place on baking sheet and coat the top of each cookie with green sprinkles, if using. Take out other cookie dough sheet and cut out 30 cookies using just a round shaped cutter. Place on baking sheet.
Bake 8-10 minutes, or until lightly brown on edges. Let cool for minute or two on baking sheet, then transfer to wire rack to cool.
When cookies are completely cooled, take the round cookies and spread a little of the raspberry preserves on each one. At this point, if you haven't used the green sprinkles, sift powdered sugar on top of each heart cut-out cookie. Lightly press it on top of jelled cookie.
Serving size is 1 cookie
If you don’t have a heart cookie cutter, use a small paring knife to make the heart shaped center of the cookie
Store leftover baked and filled cookies in the refrigerator for up to 5 days in tightly covered container
Unfilled cookies can be frozen for up to 2 months after baking in a freezer proof container or bag