Combine butter, sugar, and water in heavy saucepan and boil, stirring occasionally, until butter melts. Mix in coconut and vanilla. Cool.
Position rack in lower third of oven and preheat oven to 350 degrees. Butter jelly roll pan. Place flour in processor. Arrange butter in circle atop flour. Process until butter is incorporated, stopping once to scrape down side of work bowl. Add sugar and mix 5 seconds. Add yolks and vanilla. Blend until ball forms, about 20 seconds. Redistribute dough if necessary and process for 5 seconds to knead.
Roll dough out on jelly roll pan. Bake until beginning to color, about 15 minutes. Cool 10 minutes. Retain oven at 350 degrees.
Spread jam over pastry. Spread topping over jam. Position rack in center of oven. Bake pastry until topping is light brown and bubbly, about 20 minutes. Cool completely. Cut into 1-inch squares before serving.