Fill a small saucepan 3/4 way with water and bring to a boil. Lower to a simmer and add the raspberries. Let simmer for 15 seconds.
Use a slotted spoon to transfer the raspberries to an ice bath and let cool for 30 seconds.
Transfer to paper towel lined plate to blot excess water.
Add raspberries to a glass jar with a tight fitting lid and add the vodka. Shake, cover, and let sit in a dark and cool area for 3 to 7 days.
Vodka Collins
Halve the lemons and juice about 1 cup of lemon juice. Set aside.
Use the juiced lemons to "wipe" the rims of 4 serving glasses. To a shallow dish, add the sugar. Dip the wet glass rims into the sugar and set aside, rim side up, to dry.
Meanwhile, in a large pitcher, combine the lemon juice, vodka, simple syrup, limoncello, and sparkling water. Stir well to combine.
Divide the vodka collins amongst the serving glasses. Use a small spoon to gently spoon the raspberry extract over the vodka collins.