In a food processor or blender, process the peanuts until finely crushed.
Generously brush the bottom and sides of a 9 x 13 baking pan with oil. Line with banana leaves and brush the leaves with oil. Set aside.
In a bowl, combine glutinous rice flour and sugar.
Add water and stir into a smooth batter.
Add vanila extract and stir to distribute.
Transfer to the prepare pan, topping on the counter to remove any bubbles.
Prepare the steamer by filling with water and bring to a boil. Place the pan in the steamer and cover the steamer lid with a kitchen towel.
Steam the cake for about 20 to 30 minutes or until a toothpick inserted in the center comes out clean.
Remove from steamer and allow to slightly cool. Lightly grease working surface with oil and transfer the tikoy on the surface.
With an oiled spatula, slightly flatten tikoy while still warm.
With a lightly-greased knife or dough cutter, cut tikoy into 8 even rectangles.
Put the ube halaya in a piping bag and pipe a line or 2 along the edge of tikoy, lengthwise.
Roll the tikoy into a tight log, enclosing the filling. Dredge in crushed peanuts to fully coat.
Repeat with remaining steamed rice cake.