In a saucepan, combine the blackberries, 1/4 cup sugar and water. Bring to a boil over medium/medium-low heat, and continue to cook, stirring frequently, for about 30 minutes. The berries will break down, and the liquid will become thicker and syrupy. Once you've reduced the mixture to about 1 cup, it's ready.
Puree the hot blackberry mixture in a small food processor. Pour through a fine mesh strainer, and press as much of the fruit puree through the strainer as you can. Discard the seeds. You should have about 2/3 cup blackberry puree after straining out the seeds. Refrigerate the puree until needed.
In the same saucepan, whisk together the remaining 1/2 cup sugar with the milk, 1 cup of cream, the egg yolks and vanilla.
Cook over medium heat, whisking constantly, until the custard starts to steam and bubble around the edges, but don't let it come to a full boil.
Remove the custard from the heat, and pour through a fine mesh strainer to remove any bits of cooked egg.
Whisk the strained blackberry puree into the custard.
Refrigerate until thoroughly chilled, preferably overnight.
When you're ready to churn your ice cream, use an electric mixer to whip the remaining 1 cup heavy whipping cream until thick, soft peaks form. Whisk the whipped cream into the chilled custard.
Pour the custard into your ice cream maker, and churn according to the manufacturer's instructions. During the last minute of churning, add the vodka.
Fold the pie crust pieces into the churned ice cream, and transfer the ice cream to lidded ice cream containers.
Freeze until firm, at least 8 hours, or overnight.