Preheat oven to 325° (convection not recommended). In a 2- to 3-quart pan over medium heat, stir cream, milk, and brown sugar until sugar is dissolved, 2 to 4 minutes. Remove from heat.
In a bowl, whisk egg yolks until light yellow. Add granulated sugar and whisk until blended. Gradually whisk a fourth of the hot cream mixture into the egg mixture. Then slowly whisk in remaining cream mixture and the pumpkin, chai, orange peel, and vanilla.
Divide mixture among six ramekins (3/4 cup). Set in a 12- by 16-inch roasting pan at least 2 inches deep. Set pan in oven and pour in boiling water to halfway up sides of ramekins.
Bake until custards barely jiggle when gently shaken, 45 to 50 minutes. Lift ramekins out of water and let cool on racks for 30 minutes, then chill until cold, at least 1 hour. Cover when cold.
Shortly before serving, garnish with shards of pumpkin seed brittle.
Pumpkin seed brittle: In a heavy 6- to 8-inch frying pan over medium-high heat, stir 1/3 cup sugar and 1/4 cup water until sugar is dissolved, 1 to 2 minutes. Cook without stirring, shaking pan often, until mixture is a deep amber color, 5 to 10 minutes. Remove from heat and stir in 1/2 cup hulled roasted pumpkin seeds (sometimes sold as pepitas). Pour onto a 12- by 15-inch piece of buttered foil and spread thin. Let cool until hard, 6 to 10 minutes. Cut or break brittle into about 1/2-inch shards. Store airtight, if not using at once.