Put the flour and butter in a food processor and blend until the mixture resembles bread crumbs. Add the sugar, egg yolks, and vanilla bean paste and blend until the mixture comes together to form a smooth dough. Wrap in plastic wrap and chill for at least 1 hour.
Trace and cut out a cocktail glass shape from a picture, about 10 x 8 cm (4 x 3¼ inches), for use as a template. Grease 2 baking sheets. Roll out the cookie dough on a lightly floured surface. Lay the template over the dough and, using a small, sharp knife or scalpel, cut around it. Place on the baking sheets, spacing them slightly apart, and reroll the trimmings to make 16 in all.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 15 minutes, or until pale golden. Transfer to a wire rack to cool. Beat the food colouring into the buttercream and put half in a piping bag fitted with a fine plain nozzle. Spread a little frosting across the centre of the cookies so they look like half-filled glasses. Pipe an outline of frosting around the cookie edges. Scatter the glass cavity area with sugar sprinkles. Pipe frosting dots for the bubbles and sprinkle with the pink-tinted silver balls.