Preheat the oven to 375°F. Bring a large pot of water to a boil. Dip the peaches into the water for 15-30 seconds. Remove from the water and slip off the skin. Cut the peaches in half, remove the pits, and slice into 1/3-inch thick slices. Place in a large bowl. Toss the peaches with the sugar and flour and pour them into a 2-quart ceramic or glass baking dish. Set aside and make the crumble topping.
Toast the nuts for 6 minutes. Let cool and chop. In a medium mixing bowl, combine the nuts, flour, brown sugar, granulated sugar, sea salt, cinnamon, cardamom, and vanilla powder. Add the cubed butter and work it into the flour mixture with your fingers until it has a crumbly consistency. (If you make it ahead of time, store it in the fridge until you are ready to bake. You can also store it in the freezer for up to 2 months.)
Pour the crumble topping over the peaches and bake in the oven for 40-55 minutes (rotating once or twice). Remove from the oven and let cool slightly. Serve with ice cream or freshly whipped cream.