Dull the whole top surface of the bar with a belt sander to get it flat and dull. Wipe up the dust.
Measure the length of the surface and mark the middle. Use your square and pencil to make a line across the middle of the width.
Spread thinset mortar over the whole surface with a notched trowel.
Press trim tiles along the front edge, beginning at the center and building to the sides. Arrange the tiles so the finished edges face forward. Set spacers between them as you set them. Proceed around all the open edges of the surface, cutting the last tiles to fit as needed on a tile cutter. Note that if the bar surface is open on all sides, with no side that's against a wall or backsplash, you need to set trim tiles around the entire perimeter.
Set standard tiles behind the first row of trim tiles, starting at the middle line and building to the sides. Repeat the process, setting the tiles row by row, beginning each course at the center working to the sides. Set spacers between all of them and cut the end tiles as needed. Cover the entire surface.
Allow the mortar to set overnight. Pull out the spacers.
Grout the tiles, pressing the grout into the spaces between them with a grout float, scraping it from the surface. Wipe up the excess grout with a damp sponge.