Preheat oven to 350°F. Butter 11x7x2-inch metal baking pan. Blend first 4 ingredients in processor. Add butter. Using on/off turns, blend until coarse meal forms. Add 1 tablespoon ice water and egg yolk. Blend until moist clumps form. Press dough onto bottom of pan; pierce all over with fork. Bake until golden, piercing if crust bubbles, about 20 minutes. Cool completely.
Whisk ingredients in medium saucepan over medium heat until sugar dissolves, butter melts, and mixture comes to gentle boil. Boil very gently until caramel is thickened, stirring constantly, about 6 minutes. Pour caramel evenly over crust; cool 15 minutes to set.
Melt chocolate and cream in microwave on defrost in 30-second intervals, stirring in between. Spread chocolate over warm caramel; sprinkle with sea salt. Refrigerate until chocolate is set, at least 1 hour, but preferably overnight.