Line 2 baking sheets with parchment or silicone liners.
In large bowl, beat butter until creamy. With mixer on low, beat in 3½ cups sugar, 1 tablespoon milk/cream, and extract until creamy and smooth (add food coloring at this point*). If it seems dry, add a teaspoon at a time more of milk, mixing well after. The consistency should be like playdough and not sticking to your fingers.
Turn the dough out onto a work surface dusted with powdered sugar and knead until smooth and satiny, adding more sugar as needed. Cover the dough with a slightly damp towel to keep it from drying out.
Adding more powdered sugar as needed, portion out 1⁄8 to ¼ cupfuls of the dough and roll into two 1/2-inch-thick ropes. Cut each rope into 1/2 to 3/4 inch pieces.
Carefully transfer mints to prepared baking sheet with a spatula (the mints will be soft). Repeat with remaining dough.
Let air-dry at room temperature anywhere from 12 hours to 2-3 days until firm enough to handle.** The outside will be firm, but the insides will be soft and creamy. Transfer the mints to covered containers or bags.
Notes
*Add optional food coloring at this point by squirting 7-12 drops (depending on color) and mixing until almost uniform (it may not completely mix here, but will as you knead).**Drying time is dependent on the size of your mints and the temperature and humidity at the time of making. Storage
Room Temperature: The mints will last in a jar at room temperature for at least a couple weeks. For longer storage, place in the fridge.
Refrigeration: For storage up to 3-4 weeks, keep in an airtight container in the fridge.
Freezing: Flash freeze them in a single layer. Place them in a freezer bag or airtight container (single layers, separated by wax or parchment paper) and freeze for two to three months. To defrost: spread the frozen mints onto a baking sheet or large platter, separate, and let them sit for an hour. Then transfer to whatever you want to serve them in.