Prepare the crust: whisk together flour and sugar. Add mixture to a food processor (see Note) with chilled butter and pulse until mixture is crumbly. Add water and pulse until mixture comes together (it's ok if it's still a little crumbly). Press dough into your pie or tart dish (see Note). Cover with plastic wrap and chill for 20 minutes.
Preheat oven to 350°. After dough has chilled, remove plastic wrap, place a piece of tin foil over the dust and fill it with dried beans or pie weights. Bake 10 minutes. Remove beans (or pie weights) and remove tin foil. Poke a few holes in the crust with a fork. Return to oven and bake another 5-10 minutes until crust looks dry and starts to brown very slightly.
While crust is baking, prepare the filling. In a large saucepan, combine sugar, milk, eggs, and flour and whisk over medium-low heat 8-10 minutes until mixture thickens and forms soft peaks when you lift the whisk (should be the consistency of chilled pudding). When mixture is thickened, whisk in almond extract. Pour mixture into baked crust Chill 4 hours or overnight.
Before serving, top with blueberries, raspberries, and whipped cream. Sprinkle with granulated sugar, if desired. Store covered in fridge up to 2 days.
*If you don't have a food processor, you can also prepare the crust in a large bowl by using your hands to mash in the chilled butter.
**Pro Tip: when pressing the crust into the dish, place the dough in the dish and place a piece of tin foil on top. Use a flat-bottomed measuring cup or liquid measuring cup to press the dough flat and to fill the dish.
***Cook and prep time do not include chilling time which is 4 hours or overnight.