Of course Grolsch is a lager, but here's the extract recipe from Clone Brews:
4oz 2.5L German light crystal malt
2oz German Munich malt
6.5lbs M&F extra light DME
1oz Northern Brewer hops for bittering
1tsp Irish moss and 1/4oz Hallertau Hersbrucker after boiling for 45 min
1/2oz Czech Saaz hops after boiling for 50 min
Recipe recommends Wyeast's 2042 Danish lager yeast.
Maybe someone can recommend a decent substitute for fermenting at ale temps. Of course it will still be different, but you should be able to get in the ballpark. I think it would benefit from a fairly long secondary, then cold conditioning for a while.
Best of luck, and welcome to the forum!
May you go marching in three-measure time
Dressed up as asses, drunk to the nines
Swing from the rafters, shouting those songs
Gone unsung for far too long