Add the ice cream, milk, heavy cream, strawberries, and vanilla to a blender.
Blend until smooth and creamy, about 30 seconds, adding a splash more milk if it's too thick to blend.
Pour into a chilled glass and top with whipped cream and sprinkles, if desired.
Notes
Chill the glass first. Put your glass in the freezer while you blend. A cold glass keeps the shake thick and cold longer instead of melting down fast.Use ice cream you'd eat on its own. The ice cream carries most of the flavor, so a vanilla you actually like makes a better shake than a bargain brand.Soften the ice cream, but don't let it melt. A few minutes on the counter helps it blend smooth. If it melts all the way, the shake turns out thin and watery.Skip the ice. Ice cubes water the shake down as they melt. The ice cream and cold strawberries make it cold enough, so leave the ice out.Use a strong blender for frozen berries. Frozen strawberries are hard on a weak blender. A high-powered one blends them smooth without leaving chunks.Blend in short bursts. Pulse and stop instead of running the blender nonstop, which warms the shake and thins it out.