In a small bowl, combine the brown sugar and corn starch.

In your blender, blend the squash puree, milk, heavy cream, brown sugar mixture, salt, and egg yolks.

Blend until very smooth then strain through a fine sieve (or cheesecloth) into a saucepan.

Cook the squash mixture over medium heat, whisking constantly, until thickened and bubbly (about 10 minutes).

Reduce the heat to low and continue cooking and stirring for another minute or two (your pudding should be thickened but still pourable).

Strain the pudding through the sieve into a bowl (using a spatula or wooden spoon helps).

Stir vanilla extract and butter into the hot pudding until completely combined.

Let the pudding cool, then place plastic wrap on the surface, cover and refrigerate until cold.